Can you tell me what apps you have on your phone? I notice my phone warming up if I do one of these 2 things:

1. Leave foursquare open and searching for venues to check in
2. Leave one or more browser tabs open instead of holding back button to close tabs and exit the web browser

Phone always panas usually means app active/busy in the background. You have to isolate and troubleshoot, I guess. Or maybe consider a fresh OS reload if battery pulls don't help.