I had this problem for some time, and I have followed all advice found on the net including plugging the headphones in and out multiple times during a call, cleaning the headphone jack and blowing air into it. I even wiped and re-installed rom. In the end, the thing that worked for me was this: dialed to my friend's mobile number (and make sure he doesn't pick it up!) [at this stage, no sound coming through the earpiece, but can hear through speakerphone] whilst in-call, navigate to music app & play music [put volume to max] for a few seconds, then stop the music. The phone sounds in the earpiece miraculously came back. And so far it has not happened again.