Dave,
You can use any VoIP software for it, eg Skype. There are other alternatives like Ventriolo, Mumble. You'll need to use VAC (Virtual Audio Cable http://software.muzychenko.net/eng/vac.htm) to route sound from those programs to RadioBOSS - see Skype calls in RadioBOSS topic on how to setup this: http://www.djsoft.net/smf/index.php/topic,2323.0.html