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MSISDN, IMSI and ICCID Decoder

A single SIM carries three distinct identifiers that are often confused: the MSISDN is the dialable phone number, the IMSI is the subscriber identity the carrier network uses internally, and the ICCID is the serial number of the SIM card. Paste any of them below to see the components broken down. Runs entirely in your browser.

MSISDN: the dialable number

MSISDN stands for Mobile Station International Subscriber Directory Number. In practice, it is simply the phone number as you would dial it, written in international format such as +447700900000. This is the identifier a phone lookup API accepts as input and returns in its response, because it is the only one of the three that a third party is ever meant to see or handle.

An MSISDN in E.164 format breaks into two parts: the country calling code (one to three digits after the +) and the national significant number. The maximum total length is 15 digits.

IMSI: the network's internal subscriber identity

IMSI stands for International Mobile Subscriber Identity. It is a 15-digit number stored on the SIM that the carrier network uses to authenticate the subscriber and route calls, texts and data. It is not the same as the phone number. A carrier can technically reassign which MSISDN maps to a given IMSI, which is part of what makes number portability possible.

An IMSI breaks into three parts: the Mobile Country Code (MCC, three digits), the Mobile Network Code (MNC, two or three digits depending on the country), and the Mobile Subscriber Identification Number (MSIN, the remainder). Carriers treat the IMSI as sensitive network infrastructure and do not expose it through public or third-party APIs.

ICCID: the SIM card's serial number

ICCID stands for Integrated Circuit Card Identifier. It identifies the physical or virtual SIM itself, independently of which subscriber or number is assigned to it. A subscriber can move their number to a new SIM, for example when upgrading to an eSIM, which changes the ICCID while the MSISDN and the underlying account stay the same.

An ICCID is 18 to 22 digits long. It starts with the Major Industry Identifier 89 (marking it as a telecom card), followed by a country code, an issuer identifier, an individual account number, and a Luhn check digit.

IMEI: the device identifier (not a SIM identifier)

IMEI stands for International Mobile Equipment Identity. Unlike the three identifiers above, which all relate to the subscriber's SIM, the IMEI identifies the physical handset and stays with the device even if the SIM is moved. A phone lookup API does not use or return the IMEI, since it queries the network for information about the number, not the handset.

Why Telebase only works with the MSISDN

Carriers do not expose IMSI or ICCID to third-party lookup services, since both are used for network-level authentication and exposing them would be a security risk. A carrier lookup API like Telebase accepts an E.164 phone number as input and returns carrier, country, number type and active status inferred from that number, without ever touching the network-internal identifiers.

MSISDN lookup: what a number can tell you

An MSISDN lookup takes the phone number and returns what the network layer can say about it: the country, the carrier the number is currently on, whether it is a mobile, landline or VoIP line, and whether it is active. It cannot return the IMSI, the ICCID or the identity of the subscriber, because carriers do not expose those to third parties. The quickstart guide shows a first request, and the response field reference lists every field returned.