I like the idea of an built in Voice Chat but it would need its own in-game UI similar to Vent with channels and such. Problem is i can see this getting really out of hand without proper management, LS based chat, City chat, global trade channel, I'm just not sure how this would all be mitigated and workable in game.

I think third party VoIP's are the way to go for now because then it is micromanaged by the players involved and not such a massive scale.