In any multiplayer game an excellent advantage is to have the ability to actually speak with your teammates. Team chat is great but definitely takes up time and your not always sure your teammates will see what you typed. Here is a list of useful free voice communication clients that you may want to try out.

Advice for voice communications:

KISS - Keep it short and simple

And don't forget your ABC's when communicating during war time situations: Accuracy, Brevity, and Clarity Here are some Voice coms you should check out.

Site		Description
TeamSound		Nice Voice Communication originally made by gamers for gamers.
RogerWilco		A nice voice com that has been around for a while. Easy to set up and use.
Team Speak		Yet another great voice com that is available out there.