Google calls it their superphone. Unlike the iPhone, Google will sell it with a contract or they will sell it unlocked allowing the phone to be used with other carriers.
T-Mobile is the initial service provider. Verizon in the United States and Vodafone in Europe will be coming on board later, and more operators are expected.
Nexus One runs the latest version of the Android operating system, Android 2.1, which is also made by Google but runs on other phones as well.
The phone will sell for $180 with a contract or $530 unlocked.
More here.