International Mobile Subscriber Identity (IMSI)

What is IMSI?

The International Mobile Subscriber Identity (IMSI) is a unique code identifying subscribers on any cellular network in the world. It connects the data plan you have with your cellular network provider to the appropriate line of service. Whenever you need to connect, the network reads your IMSI code from the Subscriber Identity Module (SIM) card in your device. 

How does IMSI compare to other mobile network identifiers? 

IMSI isn’t the only mobile networking identifier in action. Others include ICCID and IMEI, and it’s important not to confuse the terms. 


IMSI and the Integrated Circuit Card Identification (​ICCID) are both components of a SIM profile, though they serve different purposes. The ICCID is an identifier for the SIM card itself, whereas IMSI identifies the subscriber using the SIM card. For use cases related to Internet of Things (IoT), multiple devices may share the same IMSI but have distinct ICCIDs. 


The International Mobile Equipment Identity (IMEI) allows a network to identify specific physical devices by cross-checking with a global IMEI database. ICCID identifies the SIM card itself, and IMSI identifies the subscriber. 

Other related acronyms 

The Mobile Station ISDN Number (MSISDN) essentially gives phone numbers to mobile equipment to enable phone call routing and SMS messaging support. You also have cryptographic codes like Ki (Individual Subscriber Authentication Key)​​  and ADM (Authentication Data Management) for encryption, allowing for more secure communications. 

What do the digits in an IMSI number mean? 

An IMSI code contains three sections, making up 14 or 15 digits in total: 

  • The first three digits are the mobile country code (MCC) that identifies the region of the subscriber. This MCC differs from the one ICCID uses. 

  • The next two or three digits are the mobile network code (MNC), identifying the network which initially issued the SIM card. If your device ever roams internationally, the MNC ensures your device can connect back to your home network. 

  • The remaining digits specify the line of service, or the specific subscriber. 

North American IMSI numbers are 15 digits long, while European ones are 14. 

What purposes do IMSI numbers have? 

The International Mobile Subscriber Identity plays a prominent role in international mobile phone networks. It primarily facilitates user authentication, mobile roaming, and fraud prevention. 

User authentication 

When you connect to a cellular network, your device sends the IMSI code to the network. An automatic analysis takes place to verify you are a subscriber with access or attempts to connect you to a roaming agreement if you aren’t a local subscriber. 

This process of identifying which network your mobile number attaches to is known as an IMSI Lookup, a Number Lookup, or a Home Location Register (HLR) lookup. 

Mobile roaming 

International roaming is possible in cellular networking thanks to IMSI. If the user is from another network provider and not a local one, the IMSI converts into a Global Title to check the user’s own HLR. 

Fraud prevention 

A form of identity theft involves swapping SIM cards to steal a mark’s assets. IMSI helps prevent SIM swapping because it’s specific to the SIM card itself and porting the mobile number to another SIM card does not change the IMSI code. An IMSI lookup can check whether the phone number associated with a device has changed recently. 

How does multi-IMSI work? 

It’s possible for multiple subscribers to be on the same SIM card. Network operators can provision IMSIs remotely, allowing use with a broader range of networks. Users themselves have more options of service providers in different regions this way. 

Multi-IMSI also has applications in the cellular Internet of Things market. If devices must function anywhere regardless of region, then multi-IMSI ensures they aren’t tied to a specific carrier’s local or roaming coverage. 

How does multi-IMSI compare to eUICC? 

Embedded Universal Integrated Circuit Card (eUICC) is a related technology that accomplishes the same task: allowing operability with multiple mobile network operators. 

But while eUICC can store multiple profiles, switching among them takes more effort since you effectively cancel your previous contract and must completely change your carrier. Multi-IMSI operates on a single service provider but enables switching between multiple subscriber identities, giving you access to more carriers. 

Switching is automatic, unlike in eUICC. SIM cards are also capable of choosing the ideal carrier at any time, such as one with a strong signal or a lower cost. And there’s no need to implement new APIs or integrations when a switch happens. 

What are the benefits of IMSI? 

The International Mobile Subscriber Identity (IMSI) provides several notable benefits in mobile networking and communications: 

  • Unique Identification: The IMSI provides a globally unique identifier for each mobile subscriber. This unique code simplifies processes such as billing, user authentication, and system configuration. 

  • Supports Roaming: IMSI plays a crucial role in enabling international roaming. When a user travels to a different country or region, their home network's IMSI allows them to connect to foreign networks, ensuring seamless service. 

  • Fraud Prevention: The IMSI provides a key measure for preventing fraudulent activities like SIM swapping. Since the IMSI is specific to the SIM card and not easily changed, it can be used to detect suspicious activities related to SIM card replacement. 

  • Multi-IMSI Capabilities: With multi-IMSI technology, one SIM card can contain several IMSIs, allowing it to operate with multiple network operators. This capability is especially beneficial for IoT devices that need to function in various regions and under different network operators. 

  • Network Management: The IMSI helps in efficient network management by allowing network operators to identify individual subscribers, track usage, and manage resources effectively. 

How does Sinch work with IMSI? 

Sinch utilizes IMSI (International Mobile Subscriber Identity) to enhance communication services. We offer IMSI lookup services for identity verification, fraud detection, and efficient routing. Our seamless roaming ensures uninterrupted services while traveling. With multi-IMSI support, we enable a single SIM card to work with different network operators. Leveraging IMSI capabilities, we provide secure and efficient communication services globally.