08-04-2013, 03:23 AM
Consider Google hangout. Google hangout makes for a very low latency, natural conversation (at least between people in the U.S., I do not have experience with it internationally). It's much better than any incarnation of teamspeak/vent/mumble (to their credit, they are designed with much larger concurrency in mind).
Just turn off the camera (if you have one) and it's audio-only.
Just turn off the camera (if you have one) and it's audio-only.