MSISDN (pronounced as /'em es ai es di en/ or MISS-den) is a number uniquely identifying a subscription in a Global System for Mobile communications or a Universal Mobile Telecommunications System mobile network. It is the mapping of the telephone number to the subscriber identity module in a mobile or cellular phone. This abbreviation has several interpretations, the most common one being 'Mobile Station International Subscriber Directory Number'.ITUOMAITU-T Rec. Q.1741-4 (10/2005)Dictionary for OMA Specifications ITUGSMAITU-T Rec. Q.1741-4 (10/2005)Mobile Terms & Acronyms MSISDN (pronounced as /'em es ai es di en/ or MISS-den) is a number uniquely identifying a subscription in a Global System for Mobile communications or a Universal Mobile Telecommunications System mobile network. It is the mapping of the telephone number to the subscriber identity module in a mobile or cellular phone. This abbreviation has several interpretations, the most common one being 'Mobile Station International Subscriber Directory Number'. The MSISDN and international mobile subscriber identity (IMSI) are two important numbers used for identifying a mobile subscriber. The latter is stored in the SIM, i.e. the card inserted into the mobile phone, and each IMSI uniquely identifies the mobile station, its home wireless network, and the home country of the home wireless network, while the former is the number used for routing calls to the subscriber. IMSI is often used as a key in the home location register ('subscriber database') and MSISDN is the number normally dialed to connect a call to the mobile phone. A SIM has a unique IMSI that does not change, while the MSISDN can change in time, i.e. different MSISDNs can be associated with the SIM. The MSISDN follows the numbering plan defined in the International Telecommunication Standard Sector recommendation E.164.