iPhone 4 GSM with no audio on phone calls on either end

I have an iPhone 4 GSM running 5.0.1, and recently during phone calls i have stopped receiving or sending audio. Now i know there is a problem with the headphone port however i know this is not the case in my situation. I have tried using a headset and bluetooth with no luck. The phone will make facetime calls without a hitch and i can use Skype to make voice and video calls without a problem. I have restored the phone multiple times both to a backup and setup as a new phone and still the problem resides. Every function on the phone works as expected except for calls over the AT&T 3G network. Voice control, voice memos work fine, and listening to music or watching youtube videos work as expected using the speakers on the phone as well as the headset. Anyone have any suggestions?