My problem was proximity sensor.
My problem was the proximity sensor. I don't know why ICS triggered it...perhaps just coincidence. At any rate, these things fail. Getting a replacement phone fixed it for me. The proximity sensor tells the screen to shut off when the phone is next to your face (after receiving a phone call) to save power. When you take the phone away from your face, it should go back on. Mine would not. Interesting enough, it WOULD work when in very bright light, like outdoors. So the proximity sensor works in conjuction with a light meter on the phone. I think my proximity sensor was on the top left part of the phone (HTC Rezound), and the light sensor is in the front camera on the top right part of the phone. You can test it by calling your phone and covering the sensor with your thumb to see if it makes the screen go out. Remove the thumb to see if the screen comes back on. Test in different lighting...make a new call for each test. You cannot easily see the proximity sensor...it is not as apparant as the camera...but it is there. Make sure your protective case (if you have one) does not cover it as well.
Originally Posted by Eric