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