As predicted, the device has a slide-out qwerty keyboard and a touchscreen interface. It will connect to the web using 3G (third-generation) technology and Wi-Fi.
The device will be launched simultaneously on both sides of the Atlantic, T-Mobile said.
Those in the US will be able to pre-order it from next month but it won't actually appear in the UK until November. The US price is $179 (around £97).
In the UK, it will be available for free on some contracts though you'll have to be on a price plan costing £40 per month. This will include unlimited data usage.
Developers will be able to create applications for the T-Mobile G1 that can be freely downloaded by users of the device.
This differs from the experience of customers of the Apple iPhone, who are only able to install Apple-approved applications through the iTunes store.
Android has been in development since last year and though it is Google's mobile operating system, a group called the Open Handset Alliance (OHA) has been instrumental in the project.
The OHA consists of more than 30 technology companies including eBay, Samsung and Intel as well as Google.
The launch event was attended by Google's co-founders, Larry Page and Sergey Brin.
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