Cast your mind back a year or two and you may recall that there was a time when telephones were used to make telephone calls. These days we expect far, far more from a phone than the mere ability to carry a conversation, and that's particularly true of the latest generation of Smart phone.

Where a PDA is an electronic organiser that can have the functions of a phone, a Smart phone is a phone that has the functions of a PDA. In principle a Smart phone is similar to a modern handset such as the Nokia 7250, with the addition of a touch sensitive screen and Internet functions such as Web browsing and mobile e-mail.

The Sony Ericsson P800 runs Symbian OS 7.0, which is the main rival to Microsoft's Windows Mobile 2003 for Pocket PC (which itself used to be simply called Pocket PC). You'll find Symbian inside handsets from Sony Ericsson and Nokia, as well as Motorola and Siemens. Think of it as the Linux of the mobile world.

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By now you'll appreciate that the P800 is a small mobile computer, and that means it is quite big by the standards of a basic handset, measuring 117mm long by 59mm wide by 27mm thick, and it weighs a hefty 158g. The plastic case is metallic blue in colour and there's a camera on back, but at first glance the P800 looks fairly conventional.

The first clue is in the active flip, which carries the keypad. When the flip is closed there is a viewable area of 208 x 144 pixels, but when the flip is open the screen is fully viewable at 208 x 320 pixels. The colour depth remains 12-bit, offering 4096 colours. There is a stylus for the touch screen clipped on the side of the phone to avoid getting it greasy and dirty, and there are three spare styluses in the box.

Inside the P800 there is 12MB of memory, and it has a Memory Stick Duo slot with a 16MB Stick included in the package. You also get an adapter so you can insert the Duo Stick in a standard Memory Stick slot. Transferring data couldn't be much easier, so long as you're part of Sony's Memory Stick fraternity.

The P800 come with two CDs of software. The first is a PC Suite to manage synchronization with Outlook and Notes, as well as modem drivers and a user guide. The second CD contains multimedia content, including an image editor, audio files, video clips, games and pictures.

Synchronisation with your PC or Mac is handled by the docking station and a USB connection, and you also get a chunky black nylon carry case, as well as a stereo headset and microphone.

Unfortunately we can't cover the key features without a load of alphabet soup, so here goes. The P800 supports tri-band GSM (900/1800/1900), GPRS and HSCSD 2.5G modes, SMS and MMS messaging, SMTP, POP3 and IMAP4 email.

The great variable with the P800 is the price, as it is dependant on the contract you sign. We've found it as cheap as £49.99, although Sony Ericsson tells us you shouldn't get it for less that £149.99.

This is a bulky phone that is too large for most pockets, but the feature list more than makes up for the size and weight. The single most important point is that the P800 works correctly, unlike the rival Orange SPV that has just been updated to fix a load of bugs. If you need your office in your pocket at all times, this could well be the phone for you.