You can enjoy their rich presence, apparently. No, I don't know what that means either, unless it has something to do with hot fudge.
Come the happy day when Xbox One launches, there will be some folks with the new console that happen to have Xbox Live Friends on the old one. Yes, you will be able to see them, says Microsoft's Marc Whitten. You'll even be able to enjoy their "rich presence", which suggests that Whitten's friends aren't made of the same stuff as my friends, but life would be dull if we were all the same. However if you were hoping to do anything other than text and message those poor souls in Xbox 360 land, you can forget it. Live chat cross-console is out of the question.
The problem here is sound quality. Microsoft has gone the extra mile to ensure that Xbox One's sound is better than the best. "It is night and day compared to chat on the Xbox 360," says Whitten, with audio chat that streams 24 kHz at a 16-bit resolution uncompressed both downstream and upstream. Xbox 360 doesn't have anything like that capability, so anyone using the old console won't be able to voice chat with the new one.
Whitten went on to say something a little odd about seeing friends cross-console. You ought to be able to see what your Xbox One friends are doing even if you're on 360, but "if I go back to Xbox 360 and I have more than 100 friends, it will only show me the subset of my friends who are friends with me on Xbox 360," an issue that comes with the limited 360 friends list. It's a problem that presumably will only affect a subset of players, not the whole base, but it's peculiar to think that an Xbox One player will be able to see and text, but not talk, to 360 buddies, while - under certain circumstances - 360 players won't be able to see their One friends, and will never be able to talk to them.
The friends list hasn't had all its features revealed yet, Whitten notes. "You'll see us add more in this area in the future," he says.
Source: IGN AMA