I had the same problem and am not sure if it is the screens or what? When I try and use the front camera it locks up the camera program.
I can tell you if you go to settings then General then to bottom of screen hit Reset then hit Reset all. It will ask for confirmation hit yes. This unlocks the camera and the back camera works but the front locks it up again when I try and switch to it, then I have to reset it again. I replaced the cameras tried the screens on different phones and still same problem.
Note this will only change your settings like background, ringtone etc. Not your data. easier then a restore, which did not work.