push_to_talk is a GNOME application that allows one to assign a key (by default F12) that will unmute one's microphone while pushed.
On Ubuntu, this is as easy as running sudo apt-get install python-gtk2 python-xlib.
1. Run sudo python setup.py install.
2. Run ptt.
If the application immediately closes with the message "You must log-out and log-in again for your system tray icon to appear.", log-out and log-back in again; a system settings change was required.
Changing the Push-to-talk Key
1. Right-click on the microphone icon in your system tray.
2. Click 'Set Key'.
3. Press the key you'd like to use.