You know, if you're going to include voice-chat in live multiplayer such as an FPS, wouldn't it be awesome if you treated your voice as if it were actually coming out of your character's mouth?
That is, there's a persistent sound object on the character model's head. Whenever the player talks, it sounds like it's coming from that character. Now this is only valid if the characters aren't Black Ops soldiers or something that would warrant the characters to be equipped with wireless headsets to communicate with. Excluding that though, then when the character talks, sound would be coming out of that character's mouth and into the open air.
This might seem a bit pointless, but think of the immersion factor you'd experience when you and your online buddy are in an empty warehouse, and you hear your friend's voice and it echoes just like it would if you were really in a warehouse. Or having to tell your friend to keep quiet because the alien stalking your group will hear you if you're too loud.
There are of course some communication barriers that might come into play, such as the sound of gunfire being so loud that you can't hear your friend in a firefight, but personally I think that's a convenience worth sacrificing.
Come to think of it, even if you did have a logical reason for the characters to have wireless headsets, you could occasionally occlude it by some kind of EM jamming.