I'm not a developer (I shouldn't even be posting here)
Maybe it's possible to use the light sensor for "dim/waking screen" during a call.
It would be tricky ofcourse because what if you're in a dark environment
But perhaps it's possible to let the sensor scan the intensity of light right after pressing the call/pick-up button, whether you call someone or pick up a call yourself.
Since I don't have any experience in developing whatsoever, I hope this idea may be a great pain in the *** / project.
P.S. It's a shame we haven't got a proximity sensor, but we do have Android