OpenArena supports a Voice chat (VoIP) feature. This allows you to use a microphone to talk with the other players, instead of the classic text chat (of course, text chat will be available anyway). In the original Quake III Arena, you needed an external software (for example Roger Wilco or TeamSpeak) to do this. ioquake engine (the one OpenArena is based on) added simple support for Mumble VoIP application (official site): starting Mumble before the game, and then launching it with +set cl_useMumble 1 option, ioquake3 engine should inform the VoIP software about your in-game position (if the played map contains location names), but everything else depends completely from Mumble configuration and features. More important, ioquake3 (thus, OpenArena) added a built-in VoIP feature, so you don