[Admins]

The Graal voice chat support uses client-to-client communication, so it doesn't slow down the server and is quite fast, although it will not work on all computers (because of firewalls or proxys) and uses as more bandwidth as more people are near you since it needs to send a voice packet to each player. The better way to do voice chat is to use a server which is receiving your voice, is mixing it and send back the voice stream to you. That way it would always take the same bandwidth (GSM would be 13kbit x 2) and it would work for everyone since the server is not behind a proxy. The only disadvantage of this is that it requires a server. Good would be that everyone could configure what bandwidth the incoming and outgoing streams take independently from the other players.
It's not the highest priority right now though to implement such a system. There are some interesting open source projects doing such things (e.g. gnomemeeting) which could be used.