Boy Genius Report got their hands on this internal memo from T-Mobile regarding the upcoming Google Nexus phone. So you don't get get eyestrain, we'll paraphrase it for you: Google will launch the Nexus in January, selling it directly over the Web. They'll share troubleshooting/support duties with manufacturer HTC. T-Mobile will then gladly provide you with service (which is no different than their policy regarding ANY unlocked phone).
No word on phone pricing, especially with this "a la carte" approach, but there's always the possibility that T-Mobile might opt for their own subsidized Nexus offer sometime in the future.