MSISDN

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MSISDN stands for Mobile Station International Subscriber Directory Number. It is the dialable phone number used to reach a mobile SIM on GSM/UMTS networks. The MSISDN links to the SIM’s identity (IMSI) inside the network.

IMSI and MSISDN are two different numbers. The IMSI is stored on the SIM card and uniquely identifies the subscriber, the home network, and the country. The MSISDN is the number you actually dial to call the mobile phone. A SIM can keep the same IMSI, but its MSISDN can change if the phone number changes.

Format and length are defined by the ITU’s E.164 standard. An MSISDN can have up to 15 digits, with 1 to 3 digits for the country code and the rest for the national number. The international dialing prefix (like 00) is not part of the MSISDN itself. When writing internationally, the number is often shown with a leading plus, for example +8801500121121, where 880 is the country code and the rest is the national number.

In short: the MSISDN is the subscriber’s dialable phone number, while the IMSI is the unique subscriber identity stored on the SIM. The MSISDN can change over time; the IMSI stays the same.