As technology continues to shrink, more features are being packed into these small mobile devices, making navigation and ease-of-use more important. This week, I tested the Motorola ROKR E8, which costs $199 with a two-year T-Mobile service agreement and makes a real attempt to be more user-friendly. The device, which comes out on July 7, isn’t much bigger than a typical cellphone but its standout feature is its keyboard, which dynamically changes to accommodate whatever you’re doing at the time, revealing only buttons that would be of use to that particular function.

The secret sauce on the ROKR E8 is its keyboard, which changes when it’s used as a phone, music device and camera.

The surface of the ROKR E8 has no physical keys at all. In its off or resting state, in fact, it’s just a black surface with rows of tiny, unlabeled bumps. But this surface is actually divided into two: The top half works like a typical cellphone display while the bottom half projects virtual keys onto its surface and uses the rows of bumps to give these keys a physical presence.

When making a call or sending a text message, the ROKR’s surface displays a regular phone keypad. But as soon as a music shortcut button is pressed, the surface morphs into five buttons for music navigation: play/pause, seek forward, seek backward, shuffle and repeat. Pressing another shortcut button to start the ROKR’s camera mode shows four buttons for zooming in or out, switching to playback mode or changing to video. Motorola (MOT) calls this its ModeShift technology. Though the lower half of the ROKR can be considered a touch device, objects can’t be manipulated with gestures like pinching or dragging as with the Apple (AAPL) iPhone’s multitouch screen.

Overall, I found that the ROKR E8’s dynamic keyboard gave me a real advantage in figuring out how to use the multi-functionality of the phone. Its changing keyboard eliminated a lot of guesswork and time that I may have spent hunting through menus for a command. And true to its name, the ROKR (pronounced “rocker”) is focused on its music phone functionality with an FM radio, a neatly organized music menu and a speaker that has convincingly simulated surround-sound effects.

But this ROKR didn’t always jam out in perfect pitch. A touch-sensitive semicircle in the center is meant to make scrolling through long lists easier — much like Apple Inc.’s iPod wheel. But because this tool on the ROKR isn’t a full circle, scrolling felt unsatisfying. You also can’t buy songs with the ROKR, or even mark songs for purchasing later on a PC.

And while the morphing buttons look futuristic and hip, I experienced a few instances when the phone was slow to react after I touched a button, as when I touched the seek forward button while listening to music or when I chose to open an MMS message I sent to a friend.

Twenty-two tiny bumps dot half of the ROKR’s surface, and the surface below each bump vibrates when it’s touched to provide sensory feedback. Nothing is ever physically pressed down, though the vibration response leads you to think otherwise.

A smart switch on the side can be held down to turn it on or off, or switched into the upward position to lock the device, preventing accidental calls or battery drain.

The ROKR E8 runs on T-Mobile’s (DT) GPRS/EDGE connection, which felt sluggish at times. And not even the dynamic keyboard on this device could help make email or instant messaging easier.

It has a two-megapixel still camera with an 8x digital zoom that can change into video-camera mode in one step. Two gigabytes of memory are built into the ROKR, and more memory can be added via a microSD card slot, which is hidden beneath a back panel. A one-gigabyte microSD card comes with the ROKR. Without this card, the internal memory will hold about 1,500 songs.

With help from a USB cord and Windows (MSFT) Media Player 11, I transferred over 200 MP3s onto my ROKR. Album art that transferred with my songs appeared on-screen as songs played, and the speaker gave off a powerful sound. Built-in stereo Bluetooth can send tunes to Bluetooth-enabled stereo speakers, and it took me just a few seconds to pair my ROKR with Motorola’s EQ5 speakers.

A preloaded program by Shazam lets users hold the ROKR up to any speaker playing a song, and in 30 seconds, identifies the track title, artist, and album art. I held the ROKR up to my alarm clock radio and it worked perfectly. But once these songs are recognized, the track data can’t be used to buy the song or even to transfer a request to buy that song to a PC for buying online at another time.

The ROKR’s FM radio will work only if its included stereo headset is plugged in because the headset has the radio antenna. But once the headset is plugged in, the radio will play via the ROKR’s speaker.

The ROKR E8 has an audio technology called Crystal Talk, which Motorola says allows your phone to perform better in loud environments. Even if the person on the other end of your phone is in a noisy place, the company says Crystal Talk will raise the volume to improve the call. I tested this by speaking to someone on the ROKR while turning a hairdryer on beside the phone. I then used a regular Razr cellphone. The person on the other end said that the ROKR sounded slightly, but noticeably, better.

Motorola’s ROKR E8 is a head-turning phone with many built-in advances that give it a smarter interface. One might wonder what other ModeShift functions the company will integrate into its devices in the future, such as a full QWERTY keyboard. The overall idea of a dynamic keyboard is a step ahead for small devices. It forces the phone to work more intuitively and improves navigation while looking stylishly sleek at the same time.

Edited by Walter S. Mossberg.

Write to Katherine Boehret at mossbergsolution@wsj.com

Digital Cameras

Megapixels: This term describes the highest resolution photo a camera can take. Often mistaken as the most important factor in a digital camera, a high megapixel count — such as 10MP or more — isn’t necessary for the average user unless he or she plans on heavily editing or enlarging photos. Most new digicams offer between five and eight megapixels, which is usually more than enough.

Optical or Digital Zoom: Optical zoom, determined by the physical movement of a lens, matters much more than digital zoom, which digitally alters an image using the camera’s internal computer. Camera companies still try to confuse potential buyers by listing a camera’s total zoom, or the optical and digital zooms multiplied together. Ignore total zoom numbers and instead focus on optical, which now averages around 5x for many new cameras.

Image Stabilization: When generously sized LCD viewing screens started replacing optical viewfinders, they also forced users to hold their cameras at arm’s length, making for plenty of blurry photographs. To remedy this, camera manufacturers have added image stabilization, tools once found only in high-end SLR models. Optical (also called “mechanical”) and digital image stabilization correct for unsteady hands and moving subjects, respectively. Cameras with both types advertise dual image stabilization, which corrects for both situations and costs more.

Mobile Devices

HSDPA and EVDO: HSDPA, or High Speed Downlink Packet Access, is the name for AT&T’s 3G, or third generation, mobile network that operates at roughly the speed of a slower DSL in a home. HSDPA is available in most major metropolitan areas and is seen as the competitor to Verizon and Sprint’s EVDO (Evolution Data Only) networks, though the popular iPhone runs on AT&T’s network using Wi-Fi and EDGE technology rather than HSDPA.

Multi-Touch Technology: Most popularly found on Apple’s iPhone and iPod touch, multi-touch is starting to show up in other products, such as in Microsoft’s Surface, a coffee-table-like computer. Rather than just responding to on-screen touches, this technology enables moving, resizing and zooming pictures and Web pages using one or more fingers simultaneously. Look for many more devices — mobile and otherwise — to incorporate multi-touch in the future.

GPS: Global Positioning Systems are most often found in cars — either built-in or on portable devices from companies like Garmin and TomTom. These gadgets use satellite technology to determine geographic location, and high-end models even display Web content like news and weather along with directions. GPS integration in mobile devices can be used to plot routes in cars, can help users find nearby businesses while on the go and can link friends by showing one where the other is located and what they’re doing.

Digital Music

DRM: Digital rights management is a set of standards that protect the intellectual property rights of online content like music and videos, preventing it from being illegally distributed across the Web. In the past year, Vivendi’s Universal Music Group, Apple and (most recently) Sony BMG said they will start selling DRM-free versions of songs, often for a higher price. In Apple’s iTunes store, these files are called “iTunes Plus” and aren’t restricted like other iTunes content.

MP3: MP3 files are open, without any DRM restrictions. Files that you rip (copy) from your own CDs are usually converted into MP3s, though iTunes users can automatically rip tracks into that program’s special format, called AAC. MP3 files can be uploaded to social-networking sites for sharing with friends and online communities.

These file types are protected by rights that tie them to specific players. Generally, AAC files make up the majority of tracks sold on Apple’s iTunes store and play only on Apple’s iPods; WMA files are Microsoft’s version of proprietary files.

Wi-Fi

The popularity of Wireless Fidelity, or Wi-Fi, brings this technology to more and more portable devices like the iPod Touch and Microsoft Zune and gives companies good reason to incorporate Wi-Fi receivers in new computers — laptops and desktops alike. While available in many flavors, different letters like b, g, a and n stand behind Wi-Fi’s more technical name, 802.11, to help discern one version from another according to characteristics like speed and compatibility. The latest version, “n,” offers the greatest range and speed, and “n” devices are usually compatible with earlier versions.

Televisions

HDTV: High-definition television has now become the standard, capable of displaying vastly better pictures, provided the source is also HD. Today’s more popular flat panel HD televisions are LCDs, or liquid crystal displays, though plasmas still hold their own. Recording HD content can’t be done with a regular digital video recorder; instead, a special HD recorder is required to capture this higher quality content.

480p vs. 1080i vs. 720p vs. 1080p: These numbers refer to the resolution, or sharpness, of a digital display, while “p” stands for progressive and “i” stands for interlaced. A resolution of 480p, known as EDTV or Enhanced Definition TV, is found most often in low-end plasmas or LCD screens. A TV with a resolution of 1080p is currently considered the Holy Grail, and costs the most. But 1080p pictures usually can’t be distinguished from less expensive 1080i or 720p pictures by average viewers at the typical distances from which most folks watch TV.

Blu-ray vs. HD DVD: Blu-ray and HD DVD are incompatible high-definition disc formats that continue to fight a seemingly endless battle to replace the DVD. The Blu-ray camp is led by Sony and the HD DVD camp is led by Toshiba. The two formats aren’t so different, technically speaking, but their very existence is confusing to consumers. The recent decision made by Time Warner’s Warner Bros. to use Blu-ray gives Sony’s side a boost, and now Viacom’s Paramount is rumored to be switching to Blu-ray from HD DVD. Dual-format players from Samsung and LG offer some solace.

Email: mossbergsolution@wsj.com

One of the most important trends in personal technology over the past few years has been the evolution of the humble cellphone into a true handheld computer, a device able to replicate many of the key functions of a laptop. But most of these “smart phones” have had lousy software, confusing user interfaces and clumsy music, video and photo playback. And their designers have struggled to balance screen size, keyboard usability and battery life.

Now, Apple Inc., whose digital products are hailed for their design and innovation, is jumping into this smart-phone market with the iPhone, which goes on sale in a few days after months of the most frenzied hype and speculation we have ever seen for a single technology product. Even though the phone’s minimum price is a hefty $499, people are already lining up outside Apple stores to be among the first to snag one when they go on sale Friday evening.

We have been testing the iPhone for two weeks, in multiple usage scenarios, in cities across the country. Our verdict is that, despite some flaws and feature omissions, the iPhone is, on balance, a beautiful and breakthrough handheld computer. Its software, especially, sets a new bar for the smart-phone industry, and its clever finger-touch interface, which dispenses with a stylus and most buttons, works well, though it sometimes adds steps to common functions.

The Apple phone combines intelligent voice calling, and a full-blown iPod, with a beautiful new interface for music and video playback. It offers the best Web browser we have seen on a smart phone, and robust email software. And it synchronizes easily and well with both Windows and Macintosh computers using Apple’s iTunes software.

It has the largest and highest-resolution screen of any smart phone we’ve seen, and the most internal memory by far. Yet it is one of the thinnest smart phones available and offers impressive battery life, better than its key competitors claim.

The phone is thinner than many smart phones.

It feels solid and comfortable in the hand and the way it displays photos, videos and Web pages on its gorgeous screen makes other smart phones look primitive.

The iPhone’s most controversial feature, the omission of a physical keyboard in favor of a virtual keyboard on the screen, turned out in our tests to be a nonissue, despite our deep initial skepticism. After five days of use, Walt — who did most of the testing for this review — was able to type on it as quickly and accurately as he could on the Palm Treo he has used for years. This was partly because of smart software that corrects typing errors on the fly.

But the iPhone has a major drawback: the cellphone network it uses. It only works with AT&T (formerly Cingular), won’t come in models that use Verizon or Sprint and can’t use the digital cards (called SIM cards) that would allow it to run on T-Mobile’s network. So, the phone can be a poor choice unless you are in areas where AT&T’s coverage is good. It does work overseas, but only via an AT&T roaming plan.

In addition, even when you have great AT&T coverage, the iPhone can’t run on AT&T’s fastest cellular data network. Instead, it uses a pokey network called EDGE, which is far slower than the fastest networks from Verizon or Sprint that power many other smart phones. And the initial iPhone model cannot be upgraded to use the faster networks.

The iPhone compensates by being one of the few smart phones that can also use Wi-Fi wireless networks. When you have access to Wi-Fi, the iPhone flies on the Web. Not only that, but the iPhone automatically switches from EDGE to known Wi-Fi networks when it finds them, and pops up a list of new Wi-Fi networks it encounters as you move. Walt was able to log onto paid Wi-Fi networks at Starbucks and airports, and even used a free Wi-Fi network at Fenway Park in Boston to email pictures taken during a Red Sox game.

But this Wi-Fi capability doesn’t fully make up for the lack of a fast cellular data capability, because it is impractical to keep joining and dropping short-range Wi-Fi networks while taking a long walk, or riding in a cab through a city.

AT&T is offering special monthly calling plans for the iPhone, all of which include unlimited Internet and email usage. They range from $60 to $220, depending on the number of voice minutes included. In an unusual twist, iPhone buyers won’t choose their plans and activate their phones in the store. Instead, they will do so when they first connect the iPhone to the iTunes software.

Despite its simple interface, with just four rows of colorful icons on a black background, the iPhone has too many features and functions to detail completely in this space. But here’s a rundown of the key features, with pros and cons based on our testing.

Hardware: The iPhone is simply beautiful. It is thinner than the skinny Samsung BlackJack, yet almost its entire surface is covered by a huge, vivid 3.5-inch display. There’s no physical keyboard, just a single button that takes you to the home screen. The phone is about as long as the Treo 700, the BlackBerry 8800 or the BlackJack, but it’s slightly wider than the BlackJack or Treo, and heavier than the BlackBerry and BlackJack.

The display is made of a sturdy glass, not plastic, and while it did pick up smudges, it didn’t acquire a single scratch, even though it was tossed into Walt’s pocket or briefcase, or Katie’s purse, without any protective case or holster. No scratches appeared on the rest of the body either.

There are only three buttons along the edges. On the top, there’s one that puts the phone to sleep and wakes it up. And, on the left edge, there’s a volume control and a mute switch.

One downside: Some accessories for iPods may not work properly on the iPhone. The headphone jack, which supports both stereo music and phone calls, is deeply recessed, so you may need an adapter for existing headphones. And, while the iPhone uses the standard iPod port on the bottom edge, it doesn’t recognize all car adapters for playing music, only for charging. Apple is considering a software update to fix this.

Touch-screen interface: To go through long lists of emails, contacts, or songs, you just “flick” with your finger. To select items, you tap. To enlarge photos, you “pinch” them by placing two fingers on their corners and dragging them in or out. To zoom in on portions of Web pages, you double-tap with your fingers. You cannot use a stylus for any of this. In the Web browser and photo program, if you turn the phone from a vertical to a horizontal position, the image on the screen turns as well and resizes itself to fit.

In general, we found this interface, called “multi-touch,” to be effective, practical and fun. But there’s no overall search on the iPhone (except Web searching), and no quick way to move to the top or bottom of pages (except in the Web browser). The only aid is an alphabetical scale on the right in tiny type.

There’s also no way to cut, copy, or paste text.

And the lack of dedicated hardware buttons for functions like phone, email and contacts means extra taps are needed to start using features. Also, if you are playing music while doing something else, the lack of hardware playback buttons forces you to return to the iPod program to stop the music or change a song.

Keyboard: The virtual keys are large and get larger as you touch them. Software tries to guess what you’re typing, and fix errors. Overall, it works. But the error-correction system didn’t seem as clever as the one on the BlackBerry, and you have to switch to a different keyboard view to insert a period or comma, which is annoying.

Web browsing: The iPhone is the first smart phone we’ve tested with a real, computer-grade Web browser, a version of Apple’s Safari. It displays entire Web pages, in their real layouts, and allows you to zoom in quickly by either tapping or pinching with your finger. Multiple pages can be open at the same time, and you can conduct Google or Yahoo searches from a built-in search box.

Email: The iPhone can connect with most popular consumer email services, including Yahoo, Gmail, AOL, EarthLink and others. It can also handle corporate email using Microsoft’s Exchange system, if your IT department cooperates by enabling a setting on the server.

BlackBerry email services can’t be used on an iPhone, but Yahoo Mail supplies free BlackBerry-style “push” email to iPhone users. In our test, this worked fine.

Unlike most phone email software, the iPhone’s shows a preview of each message, so you don’t have to open it. And, if there is a photo attached, it shows the photo automatically, without requiring you to click on a link to see it. It can also receive and open Microsoft Word and Excel documents and Adobe PDF files. But it doesn’t allow you to edit or save these files.

Memory: The $499 base model comes with four gigabytes of memory, and the $599 model has eight gigabytes. That’s far more than on any other smart phone, but much less than on full-size iPods. Also, there’s no slot for memory-expansion cards. Our test $599 model held 1,325 songs; a dozen videos (including a full-length movie); over 100 photos; and over 100 emails, including some attachments, and still had room left over.

Battery life: Like the iPod, but unlike most cellphones, the iPhone lacks a removable battery. So you can’t carry a spare. But its battery life is excellent. In our tests, it got seven hours and 18 minutes of continuous talk time, while the Wi-Fi was on and email was constantly being fetched in the background. That’s close to Apple’s claim of a maximum of eight hours, and far exceeds the talk time claims of other smart phones, which usually top out at five and a half hours.

The interface features \”cover flow\” technology for flipping through album covers.

For continuous music playback, again with Wi-Fi on and email being fetched, we got over 22 hours, shy of Apple’s claim of up to 24 hours, but still huge. For video playback, under the same conditions, we got just under Apple’s claim of seven hours, enough to watch four average-length movies. And, for Web browsing and other Internet functions, including sending and receiving emails, viewing Google maps and YouTube videos, we got over nine hours, well above Apple’s claim of up to six hours.

In real life, of course, you will do a mix of these things, so the best gauge might be that, in our two-week test, the iPhone generally lasted all day with a typical mix of tasks.

Phone calls: The phone interface is clean and simple, but takes more taps to reach than on many other smart phones, because there are no dedicated hardware phone buttons. You also cannot just start typing a name or number, but must scroll through a list of favorites, through your recent call list, or your entire contact list. You can also use a virtual keypad.

One great phone feature is called “visual voice mail.” It shows you the names or at least the phone numbers of people who have left you voicemail, so you can quickly listen to those you want. It’s also very easy to turn the speakerphone on and off, or to establish conference calls.

Voice call quality was good, but not great. In some places, especially in weak coverage areas, there was some muffling or garbling. But most calls were perfectly audible. The iPhone can use Bluetooth wireless headsets and it comes with wired iPod-style earbuds that include a microphone.

Google maps on the iPhone.

A downside — there’s no easy way to transfer phone numbers, via AT&T, directly from an existing phone. The iPhone is meant to sync with an address book (and calendar) on a PC.

Contacts and calendars: These are pretty straightforward and work well. The calendar lacks a week view, though a list view helps fill that gap. Contacts can be gathered into groups, but the groups can’t be used as email distribution lists.

Syncing: The iPhone syncs with both Macs and Windows PCs using iTunes, which handles not only the transfer of music and video, but also photos, contacts, calendar items and browser bookmarks. In our tests, this worked well, even on a Windows Vista machine using the latest version of Outlook as the source for contacts and appointments.

iPod: The built-in iPod handles music and video perfectly, and has all the features of a regular iPod. But the interface is entirely new. The famed scroll wheel is gone, and instead finger taps and flicking move you through your collection and virtual controls appear on the screen. There’s also a version of the “cover flow” interface which allows you to select music by flipping through album covers.

Other features: There are widgets, or small programs, for accessing weather, stock prices and Google Maps, which includes route directions, but no real-time navigation. Another widget allows you to stream videos from YouTube, and yet another serves as a notepad. There’s a photo program that displays individual pictures or slideshows.

The only add-on software Apple is allowing will be Web-based programs that must be accessed through the on-board Web browser. The company says these can be made to look just like built-in programs, but the few we tried weren’t impressive.

Missing features: The iPhone is missing some features common on some competitors. There’s no instant messaging, only standard text messaging. While its two-megapixel camera took excellent pictures in our tests, it can’t record video. Its otherwise excellent Web browser can’t fully utilize some Web sites, because it doesn’t yet support Adobe’s Flash technology. Although the phone contains a complete iPod, you can’t use your songs as ringtones. There aren’t any games, nor is there any way to directly access Apple’s iTunes Music Store.

Apple says it plans to add features to the phone over time, via free downloads, and hints that some of these holes may be filled.

Expectations for the iPhone have been so high that it can’t possibly meet them all. It isn’t for the average person who just wants a cheap, small phone for calling and texting. But, despite its network limitations, the iPhone is a whole new experience and a pleasure to use.

• Email us at mossbergsolution@wsj.com. Find all our columns and videos online free at the All Things Digital Web site: http://walt.allthingsd.com

When it comes to cool hand-held devices, one always stands out in the crowd: the T-Mobile Sidekick. You may have seen photos of Hollywood stars posing with this device like an accessory, or maybe you’ve just seen someone using one and you caught yourself wondering what it was.

The Sidekick, built for T-Mobile by Sharp Electronics Corp., doesn’t look like most common hand-helds, such as the Palm Treo or RIM BlackBerry, which are designed with a screen and keyboard lined up under one another for convenient emailing, phone use and Web browsing. Instead, the Sidekick is meant to be held horizontally and its screen must be twisted out with a dramatic, eye-catching snap in order to use its hidden keyboard underneath. In closed-keyboard position, the device can be held up to your ear vertically to use as a phone.

This week, we tested the latest version of this trendy hand-held, the Sidekick 3. It will officially launch July 10 for $300 with a two-year contract from T-Mobile USA Inc., but is available just for current T-Mobile customers starting today for 12 days.

Testing the Glam Factor

The last edition of the Sidekick — Sidekick 2 — came out almost two years ago, and plenty of improvements have been made in this product category since then, so we were expecting exciting new things from this third edition. We had fun testing the glam factor of the Sidekick 3 this week, using it in clubs, bars and taxicabs with extra screen-twisting snaps just for effect. But while our new gadget earned plenty of approving glances from those in the know, the Sidekick 3 isn’t all it could be.

The Sidekick 3’s most distinctive feature is its flip-out screen, but you can’t dial phone numbers with the screen closed.

Its new design is slightly more tapered than the chunky Sidekick 2, but that’s not saying much. Compared with the 0.45-inch thickness of the recently introduced Motorola Q, the Sidekick 3’s 0.86-inch depth isn’t anything remarkable. The more physically comparable Palm Treo 700p is 0.9 inches deep, but the Sidekick 3’s overall length outstretches the Treo by almost an inch, making it appear larger overall.

The Sidekick 3’s screen is generously sized at 2.62 inches diagonal, due in part to its horizontal layout. But the screen’s resolution is the same as it was on the Sidekick 2: a mushy 240×160 pixels. Compared with screens on other devices that offer greater sharpness and brighter colors, the Sidekick 3’s screen is a definite downer.

While many of the latest smartphones use high-speed EV-DO data networks for zippy Web browsing, the Sidekick 3 only uses EDGE — a much slower technology. When we tried to pull up articles about the World Cup, it took us at least 30 or 40 seconds to load each Web site.

New Trackball

Four navigation buttons that dot each of the screen’s corners make it easy to get around to different areas on this device. We especially liked the Sidekick 3’s trackball, which replaced the Sidekick 2’s up/down wheel so as to enable scrolling in all four directions.

But we were disappointed and a little surprised that the Sidekick’s lousy phone function hasn’t been improved with this version. Because of this device’s flip-out screen, the keyboard and numeric keypad are hidden unless the screen is out. So you can’t dial a number with the screen closed. After opening the screen and dialing, you can flip the screen in again and hold the phone up to your ear, but this back-and-forth process is tiring.

You can call people in your Contacts list with the screen closed by selecting an icon on the screen, because you don’t need access to the keypad for that. But even this process is a bit clumsy compared with the speed-dial functions on standard cellphones.

A few more bells and whistles try to spice up the Sidekick 3. These include Bluetooth, a processor four times as fast as that of the Sidekick 2, and a 1.3-megapixel camera. We found the camera easy to use, and a special button positioned on the top right edge of our Sidekick 3 worked as an easy shortcut to use the camera on quick notice.

We easily emailed photos directly from our photo gallery, using the trackball and navigational buttons to pull up an email format before swinging the screen out to type an email address using the keyboard.

Instant messaging on the Sidekick 3 is well-done, as it was on the Sidekick 2. AOL Instant Messenger, MSN Messenger and Yahoo Messenger come with the device, and we chatted with friends on AIM with ease. The keyboard, though it’s hard to get to, is generously spread out and comfortable to use after typing messages for awhile.

The Sidekick 3 also has a built-in Mini-SD memory-card slot, but we had to call tech support to learn where it was located. This card slot is inconveniently located behind the back panel of the device, meaning you have to actually remove this panel — exposing the battery — in order to use the slot. For users who want to pop their memory cards in and out, this is a real hassle.

Cutesy Extras

If you’re desperate for cutesy extras, the Sidekick 3 is loaded with them. The trackball turns different colors to indicate waiting text messages, instant messages, email or voice mail, and a multitude of sounds chime from the device just for the fun of it. Seventeen cartoon icons come loaded onto the device for pairing up with the contacts in your address book if you don’t want to use an actual photo. Even the low-battery indicator on the Sidekick chimes in a way that sounds cute.

But at the end of the day, this device is still not up to par with its competitors. In social circles where it’s considered cool, it might be worth buying. And if you have a separate phone, you can use the Sidekick 3 as a data-only device, though that means paying for, and juggling, two gadgets.

But the Sidekick 3’s poor phone, low-resolution screen and covered keyboard design left us unimpressed, even if it might be trendy. Our advice? Impress your friends with technology that works better for you, the user.

• Email: MossbergSolution@wsj.com

When it comes to smartphones that have a full keyboard and good email capability, Palm’s fast-selling Treo is the best. New devices are constantly being announced in hopes of becoming the “Treo killer.” Most of these challengers use Microsoft’s Windows Mobile software, formerly called Pocket PC, which was designed to evoke the Windows computer experience on a hand-held device.

None of these Microsoft-based devices has gained much traction, however. The most notable entry so far has been a hybrid gadget — a Treo that uses the Windows Mobile software, the 700w. But this model is mostly aimed at the computing staffs of big companies, who rigidly favor Microsoft products. For individual users, Palm still offers the Treo 650, which uses the Palm operating system and will soon be replaced by a newer Palm-based model capable of running on faster networks.

This week, we tested two of the latest Microsoft-based, would-be Treo killers: T-Mobile USA’s $400 MDA and Sprint Nextel Corp.’s $600 PPC-6700. (Both cost less when purchased with service plans.)

These new email phones have some very nice hardware features. But they suffer when compared with the Treo because of their Windows Mobile software, which often requires more clicks and greater menu navigation to get simple things done than the Palm-based Treo does.

Sprint PPC-6700 by Sprint Nextel Corp. $599.99. www.sprint.com.

The two devices are nearly identical. In fact, they’re really the same core device made by the same Asian manufacturer, HTC Corp. Sure, there are various small physical differences between the two, such as their different styluses and navigation buttons. But they both offer the same two striking features: a generous 2.8-inch color LCD screen that can switch automatically from portrait to landscape view; and a full QWERTY keyboard that slides out from behind this screen. Like the Treo, each offers Bluetooth short-range wireless networking. Unlike the Treo, they also offer Wi-Fi wireless networking.

The biggest difference is in their speeds over cellphone networks, and it’s a major distinction. Like the Windows-based Treo, and the forthcoming new Palm-based Treo, Sprint’s PPC-6700 works on an EV-DO network, a high-speed wireless broadband connection comparable with that of a home DSL line. T-Mobile’s MDA offers only EDGE, a drastically slower alternative that constantly reminded us that we were using a pokey mobile device, rather than a home computer.

The two devices have physically bigger screens than the Treos. But while their resolution — how much material they can display — is better than that of the Treo 700w, it’s actually less than on the Treo 650. The new contenders have much larger, roomier keyboards than the Treo does.

We tested most of the features in both devices without much trouble, synchronizing digital photos, Word documents, Internet Explorer Favorites and music files from a Dell desktop computer to each. Both have built-in 1.3-megapixel digital cameras, like that found on the Treo 700w, and the photos that we snapped around the office turned out surprisingly well. We sent them off in emails with a few simple steps.

We used each smartphone to place calls, and immediately noticed another deficiency compared with the Treo. Because the keyboards on these new models are typically hidden when the phones are held vertically, you are forced to tap soft keys on the screen to dial a phone number. With the Treo, the keyboard, which includes number keys for dialing, is always available.

The Sprint felt bulkier and more rectangular when held up to our ears compared with the T-Mobile MDA, which has more rounded-off edges. Their specs say that these two share roughly the same dimensions (about 4″ by 2″ by 1″), but the MDA’s tapered edges give it a better feel in your hand. The T-Mobile is also lighter than the Sprint, 5.29 compared with 6.1 ounces, respectively.

T-Mobile MDA by T-Mobile USA. $399.99. www.t-mobile.com

After sliding the full keyboard out, the screen view on each of the smartphones automatically switched to horizontal view for use with the keyboard. We preferred this view for Web browsing, as it offered a wider screenshot for each Web page and made it easy to type in new Web site addresses, using the keyboard.

We also tested email, which worked OK, though it was very slow on the T-Mobile device and we found the email software to be limited and clumsy compared with the Treo’s.

But it was difficult to use Windows Mobile on either device as we walked around or stood in a crowded subway. Many commands seemed to take multiple steps, and many of them required the use of the stylus, which was a pain to get out so often. By contrast, the Palm-based Treo has been engineered for minimum steps and one-handed use, with the stylus rarely required.

For instance, you can delete an email on the Palm-based Treo with just one keystroke. But, in Windows Mobile, you have to open a menu, and hit “Delete” — two keystrokes. Those extra motions really add up if you’re clearing out a lot of messages. And there are similar extra steps all over the interface.

T-Mobile’s MDA has two handy one-touch buttons at the top of its screen: one for mail and another for Internet Explorer. The Sprint didn’t have a direct access button for mail, and its Internet Explorer one-touch button was poorly positioned on the side, where we accidentally turned it on a few times — especially while sliding the keyboard back in.

Using the T-Mobile’s EDGE Internet access, it took our device a full 50 seconds to pull up the Journal’s home page, WSJ.com. The same page came up in its entirety using the Sprint PPC-6700’s EV-DO connection in only 25 seconds.

If you’re wowed by the larger screen, or need the roominess of the slide-out keyboard, these devices might appeal to you. But the T-Mobile MDA is slow; and the Sprint PPC-6700, while quite fast, is hampered by a bulky design and oddly placed navigational buttons. Both suffer from the extra steps, and frequent stylus use, dictated by their Windows software. On balance, neither of these devices offers the form and functionality of the Treo 650.

• Email: MossbergSolution@wsj.com