This is driving me insane. I mothballed my Galaxy Nexus because it heated up under light usage, and the same thing is happening to my iPhone 4S under 6.1.3. Any time I'm without WiFi, the entire right side of the phone (side with the SIM slot) begins to heat up, especially the metal band. The heat gets uncomfortable and drains battery at a ludicrous rate. The only app open is Safari sporadically loading lightweight webpages, and the phone kills itself trying to keep up. Does anyone have a fix?