I haven't seen any details on this from game-to-game. I assume it'll be uniform - if present at all. I always enjoyed hearing the enemy team talking in the lower levels of the main Headlong base as they're planning their attack. In-game voice has been all over the place depending on which game you're playing over the years. I think H2 nailed it. Oh, you're close? I can hear you. Makes sense.

Ahhhh... and then there is party chat -_-