I've used about three different Otterbox Defender cases over the course of my iPhone 4, and have never had any problems. However, I recently purchased a white on white Otterbox Defender case and this seems to be the only Defender that has given me problems with the proximity sensor. When I'm on a call, it does not dim the screen. I don't know if it has anything to do specifically with the plastic part of the defender being white, versus all my other defender cases that are black on the plastic part. I don't know. Anyone else run into this problem by chance?