A voice-over-Wi-Fi feature makes the already excellent BlackBerry Curve even better.

First came the trim, consumer-friendly BlackBerry Curve 8300. Then came the Wi-Fi-enabled BlackBerry 8820. Now there's the BlackBerry Curve 8320, an impressive PDA phone that combines the best of the previous two models and has an added bonus: While the 8820 supports Wi-Fi for data only, the 8320 lets you make voice calls over wireless 802.11b/g networks too.

Physically, the RIM BlackBerry Curve 8320 is the same as the original BlackBerry Curve, though it comes in two different colours, titanium gray or gold. It features the same thin and light design, a small but very usable qwerty keyboard, a 2Mp camera, and a gorgeous 320-by-240 display.

The biggest news is under the hood. In addition to support for GSM voice and EDGE data networks, the RIM BlackBerry Curve 8320 adds Wi-Fi with UMA - a technology that allows you to make voice calls over Wi-Fi.

We tested the RIM BlackBerry Curve 8320 in the US using one of T-Mobile's [email protected] wireless routers, manufactured by Linksys. Using the BlackBerry Curve 8320's on-screen wizard to connect to a wireless network is a breeze; within just a few minutes, we were surfing the web and downloading files with ease. The 8320 will connect to any 802.11b/g wireless network, so you can use your existing router - or even a public hotspot - to make calls and surf the web.

T-Mobile says its router is designed to conserve your phone's battery life and to prioritise voice traffic, which should - in theory - result in better call quality. However, we noticed no significant improvement when using the T-Mobile router instead of our own Linksys wireless router. Call quality over both wireless networks was the same: decent. Voices were garbled sometimes, and we noticed an echo, just as we often did when using the phone over a regular cellular connection. Being able to make calls over Wi-Fi is a great option in areas where cellular service is spotty, though. This suggests that the RIM BlackBerry Curve 8320 was designed primarily with the US market in mind.

For both voice calls and data usage, the RIM BlackBerry Curve 8320 will default to your Wi-Fi network when it is available. Should you leave the network's range, the phone is supposed to switch your call seamlessly to the GSM network (and vice versa) - but in our tests, the experience wasn't as smooth. When we went out of range of our Wi-Fi network, calls occasionally dropped, even though cellular service was available.

Those glitches aside, the RIM BlackBerry Curve 8320 is an excellent phone. Like all BlackBerry units, it is a stellar email device, with support for 10 accounts. The included camera (which sports a flash and a 3X digital zoom) took adequate but - like many cameraphones - occasionally blurry snapshots. Among other multimedia features is an audio and video player that supports most formats (including MP3, AAC, WMA, WMV, and MP4). The player's interface is basic, but audio quality is good and video looks great. The device also has a 3.5mm headphone jack and a microSD card slot (which is inconveniently located under the phone's battery, unfortunately).