What is a Multi-IMSI SIM?
August 26, 2023

At a conceptual level, the SIM identifies the subscriber to the network and enables this identity to be securely authenticated. When a device connects to a network, the SIM in the device sends the network its IMISI, and then it passes the network a key. On the network side, there is a list of IDs and a list of corresponding keys, so the network can identify and authenticate the SIM.

Traditionally a SIM has only one set of ID and keys, tying the SIM to a specific network operator. If a user wishes to change network operators, they need to #physically change the SIM card in the device. 

📕 Multi IMSI is used to switch between the identities (IMSIs) of the SIM using just one card.

📕 Multi-IMSI holds multiple mobile subscriptions or pre-loaded IMSIs. It allows the profiles of multiple MNOs to be stored on a single SIM. When a user travels abroad, the SIM automatically detects that it is in a new country and changes to the correct IMSI. The customer can then receive calls on both numbers and receive all their charges on a single bill.

📕 It allows you to use the SIM (When Travelling) as if you’re local and hence use the network at a local price.

Multi-IMSI SIM (Source: YateHSS/HLR)

🔔 This solution is IMPORTANT for the MVNO that allows the subscribers to call in different countries cheaper. Also is IMPORTANT for IoT devices that might need to change various networks and move along different locations.

📢 Someone may ask what is the difference between Dual SIM handsets and multi-IMSI solutions.

✔ Both are an improvement on physical SIM swapping in terms of convenience and being able to receive calls on both telephone numbers. However, both have their weaknesses. For example, the Dual SIM approach does away with the physical swapping but requires a special handset (that is not widely available) and so, severely limits customer choice. Likewise, multi-IMSI solutions allow for more than two IMSIs to be used but require advanced planning to pick the correct multi-IMSI before going abroad.

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