Before delving into the new Xda Mini, it’s worth briefly covering the background of the device.

Developed by Taiwanese company HTC, the Xda Mini isn’t exclusive to O2. T-Mobile has it in the form of the MDA Vario, while Orange calls it the SPV M3000 – although interestingly, Orange doesn’t plan to release it in the UK.

You can also pick it up Sim-free as the Qtek 9100 and I-Mate K-Jam.

At first sight, the Xda Mini looks just like any other PDA. However, the screen slides out to reveal a full Qwerty keyboard.

The display also switches automatically from portrait to landscape. Despite the small keys, it’s relatively easy to type on. Alternatively, you can use the included stylus to scribble text directly onto the screen.

Running Windows Mobile 5, the Xda Mini isn’t exactly the fastest phone on the block. That said, the amount of functionality offered by this Microsoft operating system is unparalleled.

You’ll find mobile versions of Word, Excel, Windows Media Player, Internet Explorer and more. We managed to sync the XDA Mini with Outlook without any major problems, although the initial Bluetooth pairing took two or three attempts.

The claimed standby time of 200 hours appears to be very optimistic. During testing, we struggled to get the Xda Mini to last more than three days, even with limited usage.

When making calls, it doesn’t feel as comfortable as standard mobile phones. Furthermore, due to the slide-out keyboard, the Xda Mini is thicker than most PDAs, though at 160g it’s not obscenely heavy.

Although it has some drawbacks, the Xda Mini is an innovative way of getting a full Qwerty keyboard on a PDA without increasing the overall size too much.

Windows Mobile 5 can be frustratingly slow, and sadly HTC says it has no plans to release a Symbian version, but it’s packed with useful features.

Hear more about this product: PCW Product of the Week podcast