Yeah, I noticed that with the 3G once. I had a case on it that covered the sensor (weird thing was it was supposedly 3G compatible), but it covered the sensor and I thought something was wrong with the phone, but I took it out of the case to do a restore and my mom called me and I noticed the phone was working just fine. Put the case on, display dead, took it off, display fine. The top of the case I had was covering the sensor that reactivated the screen when you took it off your ear.
