I liked the BlackBerry 8820 for the AT&T network when it debuted last fall. I also liked T-Mobile's HotSpot@Home service when I tested it on the BlackBerry Curve 8320, because it allows you to make voice calls over Wi-Fi. So it stands to reason that I would like the T-Mobile version of the BlackBerry 8820, which includes support for the HotSpot@Home service. And I do.

Though it looks almost identical to the AT&T version, the T-Mobile version of the BlackBerry 8820 sports a very dark midnight blue casing, as opposed to the AT&T phone's true black. T-Mobile's 8820 includes support for UMA, so you can place calls over Wi-Fi networks as well as over GSM cellular networks. You can use the on-screen wizard to connect to any 802.11a/b/g wireless network; and when you're in Wi-Fi range, the phone will use the available network to place your calls. Doing so requires the $10-per-month HotSpot@Home service, but it might save you money in the long term, since you won't have to use the minutes on your monthly plan. It also allows you to make calls in areas where cellular coverage is spotty or unavailable.

T-Mobile sells its own routers, which are designed to prioritize voice traffic and conserve battery life. Two models--one manufactured by D-Link, and the other by Linksys--are priced at $50 each on T-Mobile's Web site. I used my own Linksys router to test the service's voice-over-Wi-Fi features, and found voice quality to be good--very similar to the voice quality I experienced when testing the Curve 8320 with a T-Mobile-branded router last year, in fact. You won't mistake it for a landline call, but voice-over-Wi-Fi call quality was at least on a par with that of cellular networks. When you leave the range of a Wi-Fi network, the phone is supposed to hand the call off to an available cellular network automatically, but this feature was more problematic. Sometimes the transition went smoothly, but other times my calls were dropped.

Many of the phone's features seem to have been designed primarily for business users. The 8820 supports Bluetooth 2.0, and (like all BlackBerry devices) it handles e-mail beautifully. It can support up to ten personal and business e-mail accounts. The full QWERTY keyboard is easy to type on, and the 320-by-240-pixel display is big and bright. Though the phone comes with built-in GPS, you need a $10-per-month subscription to TeleNav's GPS Navigator service (available through T-Mobile) to take advantage of this feature.

The 8820 includes a basic audio and video player, but it lacks a camera. Browsing the Web over an EDGE network or Wi-Fi connection is tolerable; however, the phone's browser hampers the Web experience. Even though the connection speed is okay, the browser pales in comparison to some of today's excellent mobile browsers, like the iPhone's Safari.

In our lab tests of the phone's talk-time battery life, the 8820 was still running at the 10-hour mark--our test-time ceiling. We tested the battery life when connected via a cellular network only--not when using voice over Wi-Fi.

The 8820 is available from T-Mobile for $350 with a two-year contract. If you're in the market for an excellent messaging phone that has strong business features, this one is worth considering.