# MSISDN - Mobile Station International Subscriber Directory Number MSISDN is a number uniquely identifying a subscription in a [[GSM - Global System for Mobile communication|GSM]] or a [[UMTS - Universal Mobile Telecommunications Service|UMTS]] mobile network. MSISDN and [[IMSI - International Mobile Subscriber Identity|IMSI]] are two important numbers used for identifying a mobile subscriber. The [[IMSI - International Mobile Subscriber Identity|IMSI]] is stored in the [[SIM]] (the card inserted into the mobile phone), and uniquely identifies the mobile station, its home wireless network, and the home country of the home wireless network. The MSISDN is used for routing calls to the subscriber. The [[IMSI - International Mobile Subscriber Identity|IMSI]] is often used as a key in the [[HLR - Home Location Register]] ("subscriber database") and the MSISDN is the number normally dialed to connect a call to the mobile phone. A [[SIM]] has a unique [[IMSI - International Mobile Subscriber Identity|IMSI]] that does not change, while the [[MSISDN - Mobile Station International Subscriber Directory Number|MSISDN]] can change in time, i.e. different [[MSISDN - Mobile Station International Subscriber Directory Number|MSISDN]]s can be associated with the [[SIM]].