★ Mobile Subscriber Integrated services Digital Network Number, a unique number identifying a subscription in a GSM / UMTS mobile network.

★ It is the telephone number of the SIM card in a mobile phone.

★ MSIDN and IMSI are important numbers used to identify a mobile subscriber

★ MSIDN is used for routing the calls to the subscriber, where as IMSI identifies the SIM.

★ In the HLR, the IMSI is the key, and MSIDN is the number that is dialed for connecting a call to the mobile phone.