Mobile Station International Subscriber Directory Number together with IMSI are two important numbers used for identifying a Mobile Device Phone subscriber. The IMSI is stored in the SIM/UICC, i.e. the card inserted into the mobile phone, and each
IMSI is often used as a key in the Home Location Register (HLR) ("subscriber database") and Mobile Station International Subscriber Directory Number is the number normally dialed to connect a call to the Mobile Device. While the SIM/UICC has a unique IMSI that does not change, the MSISDN can change in time, i.e. different MSISDNs can be associated with the same SIM/UICC.
The SIM/UICC contains an Integrated Circuit Card Identifier (ICCID) which contains the Primary Account Number which can then be used for Financial transactions.
Mobile Station International Subscriber Directory Number follows the numbering plan defined in the ITU-T recommendation E.164. An example of the MSISDN format is shown below: