While evaluating the SIP client fring on the iPhone it came to my attention that they were doing the registration from behind a machine in Israel. This means your authentication credentials are possibly compromised, and your audio stream may go half-way around the world and be subject to intercept by a number of different parties. Not exactly what you want from your VoIP client. Then again, if you’re paranoid about security, you won’t talk about things that really matter over VoIP anyways.