The Google Phone isn’t really a Google Phone or GPhone after all. What it will be is an open-source operating system for mobile phones. The project is called Android and it’s a a software stack for mobile devices that includes an operating system, middleware and key applications.
From the Google info page about Android:
The Open Handset Alliance, a group of more than 30 technology and mobile companies, is developing Android: the first complete, open, and free mobile platform. To help developers get started developing new applications, we’re offering an early look at the Android Software Development Kit. [Android]
In this YouTube video Sergey Brin and Steve Horowitz discuss the availability of the SDK, that it will be open source in the future, and demo some applications.