The genesis of the Google phone project is described in this Boston Globe article by Scott Kirsner.
The Open Handset Alliance will release its SDK on November 12th, 2007. The iPhone SDK will not be released until four months later. Microsoft and Symbian already have not only mature SDKs, but vigorous development communities: in mid-2007 Windows Mobile had 650 thousand registered developers, and Forum Nokia had 2 million registered individuals and 440 companies in its “Platinum Program.”
As usual with a new development environment, it’s a chicken and egg situation, but the chicken is coming out in pretty good shape; if the base platform debuts with comparable functionality to what the iPhone came out with, it’s a low-risk proposition for the phone OEMs, and Google’s magic coattails will ensure hysterical enthusiasm in the developer community.