A number of reports have been leaking in that the iPhone 3G is prone to overheating. One forum poster reported that he left his iPhone on his pocket when he fell asleep. He reportedly woke up with a burned leg. The guy reported that he quickly pulled out his phone and saw that a part of the plastic cover melted. The strange thing here is that the phone was not enabled to push emails and he also disabled the “blazing 3G speed” setting.
One comment I’ve read said that this is prone to happen if the auto-lock function of the phone is not activated. Whatever the reason for overheating though it is not a good sign.