Freeze during call on every VoIP app on 3G Data iPhone

since your using a third party app to make calls, contact the app developer or go to their support site and see if you can find your resolution.

It's not only 1 app it's all VoIP apps that freezes...

Well then contact Voip since their apps is causing your phone to freeze.

VoIP functionality depends also on the speed of 3G data from your carrier.  I suspect this is why VoIP freezes. 

This is NOT an iPhone issue.  Perhaps you'll find answers on your Carrier's help forums.

You ever figure this one out? I just started having the same problem. All VOIP apps (Talkatone, Skype, Vonage) are causing my iPhone 4S to lock up. I'm on iOS 5.1.1. The actual UI locks up, and you can't end the call or press any other buttons. Going to other apps is also impossible. The entire phone is unresponsive, this is not a data throughput issue at all (to back this up, if for some reason you aren't understanding the issue - the exact same thing is happening over WiFi). I've tried restarting the phone (I had to a few times as the phone would not work), and that has not helped.