EDIT: Below is a video of the Google I/O keynote segment where the audience was told that all 4,000 of them would receive a free Android phone and a SIM that offers unlimited data and thousands of minutes for a 30-day period. It's a variation on the Magic called Ion.

[Original post]

I'm waiting for independent verification on this (check the comments) but a recent tweet from @androidandme links to a search for io2009, and the results speak for themselves. Also see some photos of the event here.