What is an IMSI number?

Last Updated: July, 2023

IoT Glossary by Freeeway AG

Quick definition: IMSI number

IMSI or International Mobile Subscriber Identifier is a unique number of 14-15 digits. IMSI number is the key component for SIM cards as it allows Mobile Network Operators (MNOs) to identify mobile subscribers.

Introduction: IMSI meaning

As the name suggests, the International Mobile Subscriber Identifier (IMSI) is key to identifying mobile subscribers globally. The IMSI is automatically assigned to each SIM card and carries relevant information like country code, MNO code, and subscriber number.

Furthermore, the IMSI number is stored in the SIM card memory itself. The IMSI identifies the subscriber on one SIM card. But if the user ports the MSISDN (Mobile Station International Subscriber Directory Number) to another SIM card, you will get a different (unique) IMSI number assigned to that new SIM.

What is the use of IMSI?

Here are several uses of the IMSI number:

  • Identity of a subscriber

The primary use of IMSI is to identify any mobile subscribers that use a mobile network globally.

  • Registering connections with a MNOs

Any SIM that connects to the network exchanges the IMSI of the particular subscriber to help associate the device with the user.

  • Access control:

The IMSI number can be used to grant access to a particular device in the IoT network and allow it a network exchange. It can also verify the services a subscriber can access.

  • Identifying home network & roaming:

MNOs can use an IMSI number to identify a subscriber’s home network and determine if they are allowed access. Particularly for roaming, this can verify if a subscriber has a roaming agreement in place or not.

  • SIM card authentication:

While registering on a mobile network, the IMSI can help authenticate the SIM card and ensure that only the authorized subscriber can access the network.

How do I find my IMSI SIM number?

Often the IMSI number is given on the packaging of the SIM card itself while purchasing it. However, here is another easy alternative to find your IMSI:

  • Browse through the settings on your phone
  • Go to “About”
  • Go to “Status”
  • Tap of “Phone Identity”
  • There you will find your IMSI number, depending on your device.

Otherwise, you can always contact your mobile operator support to help you out by sharing your IMSI.

Are IMSI and IMEI the same?

The answer is no! In fact, both serve different purposes of identification. IMEI is to identify a particular hardware device globally. It can also help track or blacklist any particular device. IMEI is associated with the device and is stored in the device’s memory.

However, IMSI helps identify any unique SIM subscriber and has no identification of the device. Together, IMSI and IMEI can help identify which subscriber is using which equipment. IMEI number stays on the device all the time, while IMSI number follows the SIM card if it is inserted in another device.