Even though the HTC EVO 4G has not been officially released to the public just yet, the exhaustively covered Android 2.2 "Froyo" OS has already been ported to it thanks to efforts by the folks at XDA. Plus, video!
XDA user Richard Ross did the deed, posted the video, and the rest is history. It was only a few days ago, you'll remember, that this phone was successfully rooted.
Speculation about this video is that is of a phone that Google gave out to I/O participants, which would make total sense.