Millions of people can use their cell phones daily because of cellular communication. The name comes from the way individual cells are organized into a grid. Each cell is about 10 square miles, and has a base station consisting of a tower and a small building housing the radio equipment. Cell phones and base stations use low-power transmitters with limited ranges, so that the same frequencies can be reused outside the range.
All cell phones have individual codes used to identify the phone, its owner, and the service provider. Whenever you turn on your cell phone, it listens for system identification code on the control channel -- a special frequency that the phone and base stations use to communicate with each other -- to locate the base station in the cell in which you are standing. If it can't find any such code, it is out of range. This is what happens when you get a "no service" message.
Your service provider's central switching office keeps track of your phone in a database so that it always knows which cell is nearest to you, and hence your approximate location. When the office receives a call, it locates which cell you are in, picks a frequency pair for your phone to use to take the call, communicates the frequency over the control channel, and your phone and the transmission tower switch on those frequencies simultaneously, allowing you to receive the call.