If you get on a call and find you don't have any audio, you can change your audio configuration by clicking on the Settings menu from the call controls, go to Change Mic or Speakers and selecting the option other than Same as System.
If you're using a headset, it will also show as an option that you can select for audio.
You can also change your settings before you get on your call by going to:
Windows: File > Settings and selecting the audio or video tab.
OSX: Biba > Preferences and selecting the audio or video tab.