According to this Gamespot story, communication in the forthcoming MMORPG Matrix Online will use AIM. This means that people in the game will be able to communicate with people outside the game and vice-versa.
What makes this particularly appealing, I think, is that unlike other MMOGs, Matrix Online isn't 100% escapism. When you are in the Matrix, you are still the real you. You aren't playing a character completely separate from the real you. So it's entirely plausible within the game world that some friend outside could IM you and you could reply "I'm in the Matrix at the moment. Wanna join me or should I come out?"
Very cool concept.