There's a rumor floating around suggesting that ALL U.S. Android phones will eventually be updated to version 2.1, most of which will receive the update sometime in Q2 2010. The source of the rumor also suggests that because of the limitations of the varying devices, some features (such as live wallpapers) will be missing from certain phones. Additionally, some, if not all, devices will require a complete memory wipe in order to receive the update.
Something to keep in mind is that "ALL Android phones" is a pretty lofty goal, considering that the first generation Android phones (G1, myTouch) are pretty old by technology standards. It's also difficult to believe that the hardware could support the update and still run smoothly. Gizmodo expresses this sentiment in a recent post:
"Sorry to rain on your parade, G1 owners and the like, but after giving this rumor a second pass we're quite sure that it's impossible that some of the older Android phones will get the 2.1 upgrade. Some of the older hardware just can't support all the functions, so while the Droid may not be the only handset to get a 2.1 update, it definitely won't be universal for all U.S. Android phones."
As with most rumors, it's impossible to say who's right at this point, so we'll take it all with a grain of salt and let time be the ultimate judge. Hit the comments with your thoughts!