Originally Posted by reallyWTF
This might sound a little crazy, but try cleaning the proximity sensor on the front of the phone. It is located to the left of the front camera. If you have a screen protector, you should see a cut out circle to the left of the camera. I was having the same problem all day today, and went up to the store to talk to someone about the problem. After a few minutes of playing with the phone we cleaned that particular spot made a call and bam the screen stayed on. We made a few more calls and noticed that you can touch that spot with you finger and the screen will go black. So it appears that if that spot gets dirty it thinks its touching you face all the time. I have not had a chance to test this theory for long but so far so good. Give it a shot and let me know what happens.
Thanks for the tip! That seems to pan out for me as I just tried it and entering numbers during calls works fine now. I didn't realize that was where the sensor was. Now that I know where it is, I just have to remember to not block it with my hand when entering numbers on the dial pad.
Thank you so much!