Third party voice chat clients allow players to communicate in real time using a microphone and headphones. By using this kind of technology, it can free up a user's hands to continue the battle. There are many software applications that support voice chat.
XFire is a Windows only chat client. The software is targeted at games. It provides in-game Instant Messaging to other XFire users. It also has voice chat capabilities. Recent versions of BZFlag 2.0.9 have some support for XFire, namely the in-game IM.
Free and open source, http://mumble.sourceforge.net/