IMSI stands for International Mobile Subscriber Identity. It is a string of numbers that is used by Mobile Network Operators (MNOs) to identify the subscriber element of a SIM profile. When dealing with IMSIs, it’s important to understand that this number does not identify the SIM card itself, just the user of the SIM. What’s more, IMSIs aren’t necessarily unique to a single SIM; multiple SIM cards can have the same IMSI if they’re operating over the same SIM profile.
What does an IMSI number look like?
An IMSI is made up of 14-15 digits. This long string of numbers can be separated into different sections that contain identifying information. The first 2-3 digits identify the country that the SIM is used in; this is also known as the mobile country code (MCC). The following three digits, after the MCC, are the mobile network code (MNC) identifiers. The remaining numbers are a combination of unique digits that are used to identify the subscriber.
It is also used to enable the communication between your SIM and the mobile networks. When your SIM card connects your device to a mobile network, it sends the them an IMSI number along with a secret key called a ‘Ki’. This way, the network can confirm it’s your device, allowing them to authenticate it and enable data to be traversed.
