The Celio RedFly is a device that connects to Windows Mobile smartphones to give them a readable 800x480-pixel screen and a cramped but usable qwerty keyboard.

In theory, it's possible to do real work such as composing emails and editing Microsoft Office documents on a smartphone. In reality, of course, few people use their smartphones for such tasks because of the small screen and tiny keyboard.

However, Celio's RedFly brings the theory of working on mobile phones much closer to reality. Celio calls its $499 (£250) device a "mobile companion". It connects to Windows Mobile smartphones to give them a readable 800x480-pixel screen and a cramped but usable qwerty keyboard.

The result is a device that's small (25x152x228mm), light (0.9kg) and inexpensive (compared with a laptop) and that has great potential for road warriors and for IT shops that support them. If you're tired of lugging around a heavy laptop just so you can type emails, view Word documents or run PowerPoint presentations, Celio's RedFly can lighten your load considerably.

How RedFly works

The Celio RedFly is neither a laptop nor an ultramobile PC (UMPC), although its screen and keyboard are similar to those of the new generation of ultralight PCs such as the Asus Eee PC 701 and Everex CloudBook.

Rather, the Celio RedFly is more like an old-fashioned dumb terminal without its own CPU or internal storage. In operation it works like a PC remote-access package: you can run any application installed on the connected phone through the Celio RedFly.

Output is displayed on the Celio RedFly's screen. Input occurs via the keyboard and peripherals, such as a mouse, that are attached to the Celio RedFly either wirelessly or via its built-in USB ports.

Besides the Celio RedFly hardware, the other key piece of this system is a small driver that installs on the smartphone. The driver works like remote-access software. It reformats and compresses the smartphone's video output and transmits it via either USB or Bluetooth to the Celio RedFly.

Using the RedFly

The Celio RedFly is easy to use. It boots up instantly and connects with your smartphone quickly. Bluetooth connectivity means you can leave your phone in your pocket or your briefcase while you work on the Celio RedFly. The screen brightness isn't adjustable but, in our tests, we found it to be more than adequate indoors.

The Celio RedFly has two USB ports, which is likely to be enough for most users. Still, you may want to carry a small hub if you need to connect the USB cable, a mouse and a flash drive all at once. And it even has the potential to charge phones when they are connected via a USB cable. So far, though, only two phones from High Tech Computer - the Tilt and the Mogul - support this capability.

There's also a VGA connector on the Celio RedFly so you can attach it to a video projector for your PowerPoint presentation. When you do that, and if you enable Bluetooth on the phone, the phone works as a wireless remote control.

The Celio RedFly looks like a frequent flyer's dream machine. Because it doesn't have a power-sucking processor, its eight hours of rated battery life means it comes close to the road warrior's Holy Grail of being able to work from dawn until dusk. And battery life is likely to be even longer if you don't use a USB cable to connect the device to your phone instead of Bluetooth.

Also adding to its attractiveness is that the Celio RedFly is small enough to fit neatly on an airliner tray table.

The Celio RedFly used for this review was a pre-production prototype - the product will be introduced in the US in April.