I've got the opposite problem to the one raised in this question - the screen goes blank once a call is initialised and that makes it nearly impossible to end a call.
The phone's gathered plenty of dust and grime so I guess I've blocked/broken the sensor. There's a lot of online advice already out for this problem. Pressing in certain spots, clearing or cleaning the area of the sensor, holding the phone in certain ways ... none of these have worked for me.
The only workaround to control a call that I've found - short of removing the battery - is to use a bluetooth headset to end the call (proximity sensor is disabled when a bluetooth headset is connected).
Are there any better workarounds? I think I want to disable the sensor since it's clearly bust. Any way to do this? I'll take my chances with screen interference when holding it close to my ear.
Curiously, six months later the proximity sensor has ... mostly ... started to function again meaning I can usually regain the screen in the normal way. Very curiously this coincided with picking up the 7.8 update. It couldn't be the update ... could it??