Modern Warfare’s multiplayer is kind of hardcore. In fact there are hardcore playlists. So in an attempt to curb cheating in Modern Warfare 2 it appears that party chat has been disabled. This way players on opposite teams can’t communicate with each other. Between this and the no dedicated servers on the PC, Infinity Ward is really going out of their way to make Modern Warfare 2 an amazingly level playing field. Could Modern Warfare 2 be the most fair online multiplayer game ever?
Via NeoGaf, but I wont link you to the thread, it’s full of spoilers.