Most may not know it, but unreal tournament 2004 has support for in-game voice chat, and even more interesting, can make other people sound like they're in the same room you are. (ie, the closer you are to them in the game, the louder/clearer you can hear them, and they can hear you, when you're talking into the "local" channel.)
Now, this tends not to do all that much for most deathmatch internet games, although it is occasionally humourous to sneak up on an enemy player and yell "BOO" just before opening fire.
Now, how about a mod designed to be :
"a 3D first and third person perspective online nightclub for the PC."
Here it is:
http://www.esconline.org/About.html