The T-Mobile Android G1 is the first phone running Google's open-source mobile operating system and although we were pleasantly surprised, it still has a very prototype feel to it.

Having said that, it bodes very well for the future of the Android platform.

The G1 was designed by HTC and follows a very similar build to that firm’s TyTN phone. However, in keeping with the 'prototype' idea, it feels a bit like HTC weren't really sure what they would be dealing with so they threw everything at it, meaning you have a BlackBerry-style rollerball, large touchscreen and a full slide-out qwerty keyboard as input options.

One input mechanism that is conspicuously absent is a virtual keyboard. This means that even entering just one or two letters involves flicking out the keyboard, which can be cumbersome when trying to use just one hand.

The device is not exactly small, but it is relatively slim and we had no problem slipping it into a trouser pocket. The front is dominated by a 3.2in touchscreen with a 320x480 pixel resolution.

There are five buttons along the base, separated from the display, meaning they stay in place when the screen is slid away to reveal the keyboard. Buttons include a call pick up, Home, context-sensitive Menu button, back and a call put down button, which doubles as the power button.

On the top left you'll find the volume control keys and on the bottom right is the dedicated camera button. Charging and data connectivity is done through a mini USB port at the bottom of the phone.

The casing does look and feel a bit cheap, and rather than just sliding straight up or down the screen moves on a strange sprung hinge, which is quite novel but seems unnecessary. We also worry that the repeated impact of the screen with the base of the device could cause the casing to crack in time.

The keyboard is one of the best we've ever used. It is a good size, the keys are nicely spaced and have a good tactile feel to them.

The G1 should prove particularly attractive to anyone who uses several of Google's services, such as Goggle Mail, Calendar and Chat. When setting up the device for the first time, the user simply sticks in their Google username and password and every Google service they use is automatically set up on the device, meaning email, contacts, calendar and instant messaging are all immediately in place with very little fuss.

As you would expect with a Google-powered device, Maps and YouTube support is also built into the device.