I'm on an iPhone 4 - 4.1. Yesterday I was at a store and went to look at an incoming email and my iPhone displayed the temperature warning and would not respond (i.e. said to wait for it to cool down). Now - the phone was cool to the touch (not cold but not at all warm). And I hadn't really "used" the phone for quite a while. No apps were running or in the quick switch dock. I rebooted and everything was fine. Was just curious if anyone else experienced something similar before?