Let the hive mind of Engadget get that for you.
"As someone who doesn't reside in the USA, I was wondering what would be the best way to get internet for my computer in the US for a couple of weeks? If it were Europe I know I'd look for some prepaid data. Is there anything similar offered by American carriers? A MiFi or a data SIM that I can tether from would work, but I'm trying to maintain a tight budget. Help!"
I talked to a rep yesterday, and she said the same thing - "it'll be out sometime this fall". She also said that there would probably be an upgrade program for those that have the current gen HD DVR, but advised me to hold off on buying one until the mpeg 4 version comes out.