No audio on FaceTime with iPhone 4S

FaceTime seems to be messed up on my iPhone 4S. I can see and hear FaceTime calls. Other people can see me but not hear me. I've tried it with numerous contacts. The mute button is not activated. I've toggled silent mode on and off.

My MacBook does FaceTime just fine. So does my wife's iPhone 4S. Help! Any suggestions?