The XDA is a colour PocketPC device with 900/1800 GSM and GPRS fully built in and, as such, is the first of its kind. In the past, if you wanted to access the Internet or send email with such a device you had to use Bluetooth or wireless kits that usually hogged the device's Compact Flash (CF) or Secure Digital (SD) slot.

While this is innovative, the adjustments Microsoft has made to the PocketPC 2002 operating system are the real talking point. Included here is the Phone Edition, where any part of the OS that could make use of a phone connection, such as contacts databases, has been tweaked so it does exactly that. If you click on a phone number or email address, the XDA will automatically dial the number or set up Outlook's Compose Message template with the email address entered. The preinstalled Action Update software keeps the OS up to speed with the latest patches and fixes.

Included on the installation CD is a modified version of Outlook 2002, as well as drivers and Active Sync software. Installation went without a hitch and, before we knew it, the XDA was synced to our Windows XP test PC. The phone connection is protected by a four-digit PIN code, but you are only prompted for this when the device has gone through a soft reset. Were you to leave it on the train and powered up, any passer-by could run up a huge bill. The XDA is only slightly smaller than your average PocketPC PDA, but far sleeker. It's also lighter and, while this comes at the cost of a CF slot, there's still an SD slot at the base.

The fact that the antennae juts out from the sleek design is unfortunate. The stylus is stored inside the antennae and is comfortable to use and slightly longer than many others.

Possibly the best thing about the XDA is its screen. It's very bright, sharp and incredibly responsive. Unlike many PocketPCs, the viewing angle is tremendous: even at a 60 degree angle you can see the screen clearly.On the hardware side, there's very little to complain about. Intel's 206MHz Strongarm processor is coupled with 32MB of Rom. The supplied 32MB of Ram storage may not be enough for some, but any data that spills over can easily be transferred onto an SD card.

Viewing web pages through the screen was very simple, with nearly all pages easily navigable. To speed up web page download times, O2 (formerly BT Cellnet) uses a company called Bluekite to compress multimedia information, such as web page backgrounds, without any noticeable effect on your browsing capability. Download speeds were impressively fast, at 42Kbits/sec - while the rate did vary, it tended to be just as fast as a 56K PC modem.

Using GPRS connection was a bit disappointing. While connection speeds were superb, it seemed to revert to GSM at every available opportunity. This meant you had to connect in order to receive email, completely defeating the purpose of the so-called always-on connection. Switching the XDA to standby mode reduces it to a GSM-only device, so you are not alerted when an email is received. However, it does automatically switch on when it receives an SMS or phone call. We always managed to pick up a GSM signal, though at times reception was patchy.

When used as a phone, though, the XDA was excellent. It's just small enough not to be a handful when it's next to your ear and sound quality is excellent. The inbuilt speaker is loud enough to be placed on a table and used for conference calls. The buttons on the front allow you to bring up a contacts database, scroll through and dial a number without using the stylus.

The XDA is sold only through O2's network and this will remain the case for the foreseeable future. But certain retailers (such as Expansys) are selling the XDA Sim-free, although it'll cost you £750 inc VAT.