I have a Samsung Galaxy S3 SGH-T999 (Tmobile). When I had the stock ROM the phone worked fine, but now I am having the same issue with multiple ROMs.
Whenever I make or receive a phone call, the screen turns black (LED off and everything) and it will not come back on until the other person has hung up (I can't, because I have no buttons). I have tried Cyanogenmod 10.2.1 stable, Cyanogen mod 11 nightly (newest), and Paranoid Android 4.4.2 BETA 3.
I read on another forum that this may have something to do with the proximity sensor, and I went to settings>devices>more and under "Sensors and Motors" there is only vibrator intensity. I also checked the call app settings and there are not any options relating to proximity sensor. I also tried several USSD codes to check that which I found online but have been unsuccessful in getting any of those to work.
Any help would be greatly appreciated!