Mumble offers
Voice Chat capability similar to Teamspeak or Ventrilo
Go here to download Mumble for your OS -
http://sourceforge.net/projects/mumble/
Here are some instructions for getting the latest version (1.1.6) setup in ubuntu
Connect using the following settings:
server: 74.86.235.146
port: 64738
The lobby channel is accessible by anyone
To access clan channels, you need an account setup with a password. Please contact contact Dokujisan to request a password or request a channel for your clan.
Make your Mumble Push-to-talk
Configuration - Settings - Audio-Input - Transmission - Push-to-talk
Set your push-to-talk key
Configuration - Settings - Shortcuts - Push-To-Talk