Teamspeak is a voip client that allows teammates to talk to one another while playing BF2. BFSupreme's Teamspeak server has 40 available slots and a plethora of different communication channels to choose from. BFSupreme makes Teamspeak available for those who request access, just ask a member for a login and they will get you one. Once on Teamspeak you may ask to be a registered user.

If you have questions about installing and using Teamspeak go here:
TS Tutorial