Every mobile subscription has an IMSI (International Mobile Subscriber Identity). It identifies the subscriber to the network and tells the network which home operator to contact for authentication and charging. A normal SIM has one IMSI.
A Multi-IMSI SIM holds several IMSIs, each belonging to a different sponsor operator. An applet on the SIM switches between them, based on the country or network the device is in, or on instructions sent over the air (OTA) by the operator.
Why MVNOs and IoT operators use it
- Better coverage: the device can use the IMSI that has the best access agreements in each country.
- Lower roaming costs: using a local or regional IMSI can be much cheaper than roaming on one home identity.
- Avoiding permanent roaming limits: some countries and operators restrict devices that roam permanently, which matters for IoT devices that never leave a market.
- Resilience: if one sponsor has problems, devices can switch to another.
How it differs from eSIM
An eSIM (eUICC) can store several full operator profiles and download new ones remotely, using GSMA standards such as SGP.02 and the newer SGP.32 for IoT. Multi-IMSI is simpler: several identities inside one SIM application, managed by the SIM provider or MVNO. Many IoT solutions combine both, using eSIM to change the main profile and Multi-IMSI for day-to-day switching.
What Multi-IMSI means for your BSS
This is where many projects underestimate the work. The network side may switch identities smoothly, but the business systems must still show one customer, one SIM and one correct bill.
Identity and inventory
Your inventory must link one ICCID (the SIM) to several IMSIs and MSISDNs, and know which sponsor each belongs to. CRM, support tools and self-care portals should show the customer one subscription, not several.
Provisioning
Activating, suspending or terminating a SIM means updating every sponsor's HLR or HSS, plus your own systems. Provisioning flows need to handle partial failures and keep all sponsors in sync.
Charging and rating
Usage arrives under different IMSIs, sometimes from different charging interfaces or record formats. The OCS and mediation must recognize them as the same subscription, apply the right customer price and track the wholesale cost for each sponsor.
Wholesale reconciliation
Each sponsor sends its own records and invoices, often using TAP or CDR files. You need automated reconciliation between sponsor charges and your own rated usage to catch errors and protect margin.
Switching rules and security
Decide who controls switching rules, how OTA commands are secured and logged, and how you detect unusual behaviour, such as rapid switching or unexpected traffic patterns that may signal fraud.
Getting it right
Treat Multi-IMSI as a business capability, not only a SIM feature. Design identity, provisioning, charging and reconciliation together, agree clear data exchanges with each sponsor, and test end to end before launch.
I recently architected an in-house BSS portfolio covering OCS, Multi-IMSI and information security. If you are planning a Multi-IMSI launch, I can help you design the BSS side.
