Q: I got an iPhone 4S two weeks ago. Tonight it turned itself off and after a few minutes it started overheating. It was too hot to hold. I can't turn it back on. If i could, will it be safe to use?

http://support.apple.com/kb/HT2101

Operate iPhone, iPad, and iPod touch (4th generation) in a place where the temperature is between 0º and 35º C (32º to 95º F). Low- or high-temperature conditions might temporarily shorten battery life or cause the device to temporarily stop working properly.

Store the device in a place where the temperature is between -20º and 45º C (-4º to 113º F). Don’t leave the device in your car, because temperatures in parked cars can exceed this range.

When using the device or charging the battery, it is normal for it to get warm. The exterior of the device functions as a cooling surface that transfers heat from inside the device to the cooler air outside.

If the interior temperature of the device exceeds normal operating temperatures, you may experience the following as it attempts to regulate its temperature:

• Device stops charging
• Display dims
• Weak cellular signal (iPhone 4, iPad Wi-Fi + 3G, and iPad 2 Wi-Fi + 3G only)
  
• Camera flash is disabled (iPhone 4 only)
• Temperature warning screen appears with the message "iPhone needs to cool down before you can use it", "iPad needs to cool down before you can use it", or "iPod touch (4th generation) needs to cool down before you can use it" (see image):

Hold the HOME and SLEEP buttons at the same time to reboot the phone.