Why not just have a teamspeak channel for each server?
Because its in-game, and monitored. If you spout out "aliens base is 'here'!!" on public chat in Trem, you'll get a mute or maybe kick. And yes, why use a third-party client? (not to mention it seems to be notorious for team stacking purposes in team-games)
As long as games are small, people can invite personal group chats within the server as far as i know. They do this during scrims. Well, when they used to happen.
Or two mates that want one to win, so the other feeds/spies for the first. Or instead of giving the entire team an idea, the two share the glory as they win.
I think Trem chat should stay in Trem.
But, two questions:
1) Will there be PM voice chat?
2) Can IRC channel access be implemented in-game for players and admins?