How many battery powered devices do you need in your briefcase? A mobile phone, of course, perhaps a PDA, a digital camera, an MP3 player and the latest fashion item, a GPS locater, takes you to a total of five devices. Or you could take the HP approach and carry a single iPaq Mobile Messenger.

There are two models which are very similar in appearance and specification. The hw6510 reviewed here is a PDA phone with a full QWERTY keyboard and a 3-inch TFT screen with a resolution of 240 x 240 pixels.

The processor is a 312MHz Intel XScale PXA272 and it has 64MB RAM and 64MB ROM to give a total of 128MB. You can see from the dimensions of 71 x 118 x 21mm that this is a fairly wide phone, thanks to the keyboard, but it is conventionally sized for a PDA.

In that context the screen is either very large for a phone or rather small for a PDA, depending on how you're using the HP. Either way, the 179g weight (with battery) is no burden.

The second model is the hw6515 which has a 1.3-megapixel camera, like so many phones these days, but you're likely to pay a hefty £50 premium for the privilege of the camera.

The hw6510 runs Windows Mobile 2003, has Bluetooth and also comes with a copy of TomTom, because, you see, the HP hw6510 is a GPS receiver. It uses a technology called Global Locate IndoorGPS system which compensates for the weaker GPS signal that you get inside a building by aggregating signals over a short period of time. Let's face it, your position is unlikely to move much within a building, but we didn't notice any benefit from the system.

HP also includes a Quick GPS Connection utility which tells the hw6510 where it can expect to find GPS satellites. This tool should be quite useful but it is instead rather annoying as the settings expire every two days and if you're not careful they will be updated over GPRS, which could get expensive.

Also supplied is a copy of BVRP Software's GSM/GPRS Manager utility to assist connection to your nearest network, but this PDA doesn't have Wi-Fi and the SD slot is likely to be in use for your GPS map, so you'll have to switch back and forth if you wish to use wireless.

The package is rounded out by a docking station which synchronises with your PC over USB and recharges the battery, or you can use the power cord on its own when you're travelling.

On paper the iPaq hw6510 is an interesting proposition but it suffers from trying to be all things to all people. We're not great fans of PDA phones at the best of times and adding GPS means that you have a device that isn't good enough at any one task, but if you get it on contract it is incredibly cheap.