Was having problems hearing callers on the phone. I could hear the ring OK, but would answer and wouldn't hear anything. I jacked the call volume to max and could barely hear my wife on the phone. I put it on speaker and that helped, but I was at Ala Moana Center and it was pretty noisy, so it wasn't perfect, either.
The next day, while driving, the kid called me, and I couldn't hear him EITHER! Infuriating! When I stopped the car at school, I looked at the phone and SLAPPED MY HEAD IN A DUH MOMENT!
I had left the plastic on the front of the phone as a screen protector, but it completely covered the sound hole.