when your mobile phone is on the phone communicate to a base station.there are usually hundreds of base stations in cities all over the world sometimes telephone companies disgue their base stations so you dont notice them.each base stations is at the centre of a cell.all the calls and messages in thatarea go to the cell's base stations.a special base station controller tranmits the call.controllers can take a certain number of calls at the same time so if a lot of people call some of them may not be able to get through.this doesnt happen