If for some obscure reason your iPhone freezes and stop responding to any of your commands. And you′ve tried the button, switch or touchscreen input but nothing will wake up your device.
You need to reboot or reset the iPhone. Here’s how to do it:
To reset the iPhone, press and hold the Sleep/Wake button and the Home button at the same time for at least 10 seconds.
Simple? Yes, and it can save your life!
