This days seems to be VoIP (Voice over Internet Protocol) everywhere, in fact I’m looking at the alternatives to make up my mind on what to choose. Probably I will start with free calls over internet, then go with one VoIP provider, and then with real VoIP enabled phones.
But if you’re looking for privacy, look somewhere else. Just using tcdump and vomit is enough to hear VoIP conversations. Perhaps piping VoIP trough a secure channel could help, but I think it will not be a smart thing to do, because it will probably degrade voice quality and besides that, you could do nothing when using services as Skype or Brujula VoIP.