The personal identification number (PIN) is used for identification of a call number by the system. Each call number can be assigned any number of PINs. There are 15 different types of PINs, each of which (exception: PINC) can be activated by means of its own code (AMO WABE). A PIN application is initialized for each type of PIN. The predefined PIN applications can be altered or redefined by specifying additional PIN/PCODE attributes.