The microprocessor integrated in SIM cards has been specially designed to protect the services to which subscribers have access, to securely store personal data such as contact details, and to provide other applications such as sports info, mobile banking and mobile TV access amongst others. The same mobile phone networks that carry voice calls also carry data exchanged between your operator and your phone's SIM card.
This is how your mobile phone always shows the right time automatically, even when switching to or from daylight saving time. It also allows networks to locate you, so that you can receive calls wherever you are in the world. This radio transmission technology also allows your operator to update its services on your telephone in real time.