Audio is NOT a bandwidth hog at all. you can get by with a dialup connection for audio, but you need low jitter otherwise your latency will be so high..... It will be clear but the delay will annoy the hell out of you.

I have cricket wireless (you can role eyes now), I need to login into my vpn via a phone call, accept call and hit # sign. amazingly, it works even without paying for wifi on my phone. I do pay for it on my PC. I just connect to gogo, and accept the terms and I also login into messaging on my iphone. But the vpn call comes right thru.