International Mobile Subscriber Identity (IMSI) Each registered user is uniquely identified by its international mobile subscriber identity (IMSI). It is stored in the subscriber identity module (SIM). A mobile station can only be operated if a SIM with valid IMSI is inserted into equipment with a valid IMEI. International Mobile Station Equipment Identity (IMEI) It uniquely identifies a mobile station internationally. It is a kind of serial number. The IMEI is allocated by the equipment manufacturer and registered by the network operator, who stores it in the EIR. By means of IMEI one can recognize obsolete, stolen or non-functional equipment Mobile Subscriber ISDN Number (MSISDN) The real telephone number of a mobile station is the mobile subscriber ISDN number (MSISDN). It is assigned to the subscriber, such that a mobile station set can have several MSISDNs depending on the SIM
