An interesting prompt that most iPhone users are unaware of is the temperature warning that triggers under excessively hot or cold environment conditions. Recently, there have been reports circulating of an iPhone 3G and iPhone 3G S overheating issue to the point where a few white iPhone 3G S models have turned pink.
On June 25th, Apple published a “common sense” warning regarding the need for keeping both iPhone models within safe an acceptable operating temperatures. The guide explains that using the iPhone in temperatures over 95 degrees Fahrenheit - that's 35°C in the rest of the world - will trigger a Temperature Warning prompt, shown below.
For those iPhone enthusiasts who think they have mastered every menu and prompt that OS 3.0 has to offer, think again. Apple claims that if the phone falls under -4°F/-20°C or exceeds 113°F/45°C, the display will begin to dim, it will fail to charge, and it will receive a weak cellular signal. Apple also warns that exposure to direct sunlight during CPU or GPU intensive applications that warm up the device may overheat it as well.
Although the Temperature Warning menu allows users to make emergency calls if needed (although with a weak signal), it is not mentioned how much time the device will need to recover to a fully operational state.