Apple says that if the iPhone is running in high temperature environments, you could find that the unit will stop charging, get a weak signal, dim the display, or flash a temperature warning that tells you that the device needs to cool off before it can run. Apple suggests keeping the iPhone in an environment ranging from 32 degrees to 95 degrees fahrenheit (-20 to 45 degrees C). To keep your phone away from harmful heat, the manufacturer warns you not to leave your iPhone in your car, and not to use an app over a long period of time in direct sunlight (like GPS).
Is Global Warming responsible for the iPhone's overheating issue,or is it an internal problem with the phone that Apple needs to deal with? As soon as the guys at Cupertino comment, we will pass it along.
source: Apple via neowin