MSISDN stands for Mobile Station International Subscriber Directory Number. It is a unique number that identifies a mobile phone subscription in a GSM or UMTS network. Essentially, the MSISDN is the phone number associated with a SIM card and is used for routing calls and SMS messages to the subscriber. The MSISDN includes the country code (CC), the national destination code (NDC), and the subscriber number (SN), following the international numbering plan (E.164) which limits the MSISDN to a maximum of 15 digits.