In order to access the FSMTC mobile network, you must have a GSM mobile phone and a SIM card. When you call a fixed or mobile phone, a base station, fitted with a transmitter/receiver/antennae system, receives and transmits your message. This base station is connected to the telephone exchange, whose main function is to maintain the call when you leave one cell and enter another, and also collects the necessary data for billing and accounting.