Actually, I was just about to post up the EXACT same scenario...
Mine sporadically blacks out after I make an outbound call when I dont even put it up to my ear yet. I've tested it to a point where I would make an outbound call and immediately turn on the speakerphone w/o covering the proximity sensor while standing in a very lighted room. The phone blacks out as if I put the phone up to my ear.
Sometimes it gets as bad as the screen not turning back on AFTER the call ended. This is even after I've pushed the power button numerous times to turn on the screen! From that point, the only way I can get the screen on is to (1) plug in the charger, (2) wait for someone to call, or (3) do a battery-pull.
This gets soooooo annoying cuz after I make an outbound call, lets say Im calling a business that requires me to punch in numbers to be directed to the proper department, Im unable to dial those numbers as needed. This happens sporadically and I know to ensure to give light/distance to the proximity sensor....
I've tried to look for a setting to the sensor or outbound calls, but no luck...
Can anyone direct me to the proper fix?