In mobile telecommunications, two important identifiers often come up: the IMSI and the phone number. Though they both relate to mobile devices and users, they serve very different purposes and operate at different layers within the mobile network system. Understanding the distinction between an IMSI and a phone number is key to grasping how mobile communication works.
1. What is an IMSI?
IMSI stands for International Mobile Subscriber Identity. It is a unique number stored on a mobile device’s SIM card (Subscriber Identity Module) that identifies a subscriber within the mobile network.
The IMSI is typically 15 digits long and consists of three parts:
MCC (Mobile Country Code): The first 3 digits identify the country.
MNC (Mobile Network Code): The next 2-3 digits identify the mobile network operator.
MSIN (Mobile Subscriber Identification Number): The remaining recent mobile phone number data digits uniquely identify the subscriber within the operator’s network.
The IMSI is a core component of the mobile network’s authentication process. When you turn on your phone, it uses the IMSI to register with the cellular network, allowing the operator to recognize who you are, authenticate your subscription, and provide you with services.
2. What is a Phone Number?
A phone number is the public identifier used to route calls and messages to a specific user on a telephone network. It is the number that people dial to reach you and the one you share with contacts.
Phone numbers follow national and international numbering plans, such as the E.164 format, which includes a country code, area or operator code, and subscriber number.
Unlike the IMSI, the phone number is not stored on the SIM card but is assigned by the telecom operator and often linked to the subscriber’s account.
The phone number is primarily used for user-facing communication—it’s what people see and use to call or message you.
3. Key Differences Between IMSI and Phone Number
Aspect IMSI Phone Number
Purpose Identifies subscriber within the mobile network for authentication and service provisioning. Routes calls and messages to the user; public contact identifier.
Visibility Usually hidden from users; used internally by the network. Visible to users; shared publicly or privately to communicate.
Format Numeric, fixed length (usually 15 digits), includes country and network codes. Varies by country, includes country code and subscriber number.
Location Stored on the SIM card. Stored in the operator’s database, linked to the subscriber’s account.
Changeability Remains the same as long as the SIM card is used. Can be changed or ported to different operators independently of the SIM.
Security Role Crucial for authenticating subscriber identity to prevent fraud. Used for call and SMS routing but does not authenticate the user.
4. How IMSI and Phone Number Work Together
When you make or receive a call:
The phone uses the IMSI to authenticate and connect to the mobile network.
The network uses the phone number to route the call or message to the correct device.
Although they are linked, these identifiers serve different functions: the IMSI is a secure internal identifier for network operations, while the phone number is the public-facing identifier for communication.
Conclusion
In summary, the IMSI is a secret, permanent subscriber identifier stored on your SIM card, essential for network authentication and service delivery. The phone number is the public address that allows others to contact you via calls or messages. Both are fundamental to mobile telephony but operate at different levels—IMSI inside the network infrastructure, and phone number in the user communication layer.