Why your cellphone wont work during a disaster?

Some disasters can interrupt the communication services we take for granted and use every day.  Too many telephones off the hook – whether shaken off by an earthquake or picked up by too many people trying to reach concerned friends and relatives – can overload the local phone system.  Similarly, too many customers trying to make calls on their cellular phones can bring that system to a halt.  Infrastructure damage (e.g., lines down, structural damage at a central office) can likewise render our telephones unusable.