Except make a call, you cellphone could do another 5 things that you may not know.

First, when you come across urgent things

The rescue number that you could dial is 112, no matter where you are. When you find there is no mobilephone signal and you meet something urgent, always try 112, it will help you a lot and make other ones knows what's you meet.

But other four, smart friends, why not tell your idea out?