So I switched to a white iPhone 4 and have been using a Otterbox Defender on my black one. I didn't sell the case with it because I was going to use it for the white one. I've been having proximity sensor issues since I got the white one and was about to take it in until I decided to make some calls without the case. Presto, no issues at all. I put the iPhone in the case, made a call, held my thumb over the entire hole for the sensor and nothing. Guess I'll write Otterbox about this. Just FYI.