Telecommunications system

摘要

In a telecommunications system such as a global mobile telephone network in which each subscriber unit includes a Subscriber Identity Module (SIM card), each SIM card has fixed memory locations (22), to which data can be addressed over the air. The locations (22) can be accessed from the subscriber unit on the entry of short simple codes, each associated with one of the locations. Further fixed memory locations (24) can be read over the air only when the subscriber enters a personal identification number. Also, the SIM contains means which are operable to act on receipt of a signal, from the user of the subscriber unit or from a host station, to determine and undertake an appropriate response to the signal.