Multi-IMSI puts more than one subscriber identity on a single SIM, so the same device attaches as a local subscriber on several networks instead of roaming on one. The IMSI is the number of up to 15 digits that identifies a subscription inside the network; the phone number (MSISDN) is a separate thing mapped to it in the home operator’s HLR or HSS. It earns its keep when a large share of traffic sits permanently outside the home network, cross-border IoT above all.
A logistics company puts tracking units on 4,000 trailers that cross from Spain into Morocco and back every week. On a normal SIM from a Spanish host, each unit is a roamer for half its life, paying whatever the host’s agreement with the Moroccan operator says, and the MVNO that sold the contract has no say in that rate. Put a second IMSI on the same SIM, one belonging to an operator with a good wholesale deal in Morocco, and the unit stops being a roamer the moment it crosses the border. That is the whole idea behind multi-IMSI. What follows is what it involves technically, how it differs from three things it is often confused with, and what it does to the billing system that has to make sense of the result.
What an IMSI is, and why one is sometimes not enough
The International Mobile Subscriber Identity is the number that identifies a subscription inside the mobile network. It is up to 15 digits: a three-digit mobile country code, a two- or three-digit mobile network code, and a subscriber number assigned by the operator. It lives on the SIM with the authentication key (Ki), and it is what the SIM presents when the device attaches to a network. The phone number (MSISDN) is a separate thing, mapped to the IMSI in the home operator’s HLR or HSS.
The country and network codes are what make roaming work, and what make it expensive. A visited network reads them, works out which home operator the subscriber belongs to, and sends the authentication request there. Whether the device is allowed on, and at what wholesale rate, is decided by the roaming agreement between the visited network and that home operator. One IMSI means one home operator and one set of roaming agreements, whatever the brand on the SIM says.
For an MVNO that means the host’s roaming footprint and inter-operator tariffs are inherited wholesale. A Light MVNO usually gets a subset of them, at a mark-up, often with destinations blocked. Fine for a domestic consumer brand. A problem for anyone whose subscribers or devices spend a large share of their time outside the host’s country.
How a multi-IMSI SIM works
A multi-IMSI SIM carries several IMSI and key pairs from several home operators, plus a small applet that decides which one to present. The applet reads the country code of the network the device can see and picks the IMSI whose home operator has the best deal there, according to a rule table on the card. If registration with the preferred IMSI fails, it falls back to the next one. The rules can be updated over the air, so a new sponsor agreement, or a change in which IMSI is cheapest in a country, reaches the whole fleet without touching a device.
From the visited network’s point of view nothing unusual is happening. It sees a roamer from operator B, authenticates against operator B’s HSS, and bills operator B at their agreed rate. Operator B, the sponsor, passes the usage to the MVNO under a wholesale contract. The subscriber sees one brand and one balance. The MSISDN may differ per IMSI, which the platform has to handle for calls and SMS, but data, which is most of the traffic in the cases that justify multi-IMSI, does not care.
The same mechanism works on an eSIM. A multi-IMSI profile is downloaded to the eUICC like any other profile, and the applet inside it does the switching. This is different from a device holding several complete operator profiles, which we come to below.
The economics follow from who negotiates the rate. A specialist with millions of connections concentrated in a few corridors gets better wholesale terms in those corridors than a generalist host does, and multi-IMSI lets an MVNO borrow that position country by country. Coverage improves for the same reason: a sponsor with agreements where the host has none turns a dead zone into a served one.
Multi-IMSI, sponsored roaming, eSIM multi-profile and classic roaming compared
These four terms get used interchangeably in sales conversations and they should not be. Two describe a technical mechanism, one a commercial arrangement, and the fourth is the default the others are trying to improve on.
Sponsored roaming is the commercial side: an MVNO uses a partner’s IMSI range and, with it, the partner’s roaming agreements. It does not require several IMSIs on the card; a SIM with a single sponsor IMSI is a sponsored roaming SIM. Most multi-IMSI deployments are built from several sponsored roaming relationships, which is why the terms travel together.
eSIM multi-profile means the eUICC holds several complete operator profiles, each with its own IMSI, key and applets, downloaded through an SM-DP+ or the M2M and IoT remote provisioning variants. Switching is a profile enable and disable operation, slower and more visible than an applet swapping IMSIs, and each profile is normally a separate subscription in a separate operator’s BSS.
National roaming is a different animal: an agreement between operators within one country so that subscribers of one can use the other’s radio network where the first has no coverage. Single IMSI, no SIM logic, decided in the core network.
| Classic roaming | Sponsored roaming | Multi-IMSI | eSIM multi-profile | |
|---|---|---|---|---|
| Who holds the roaming agreements | the host MNO | the sponsor whose IMSI is on the SIM | each sponsor, one per IMSI | each operator whose profile is loaded |
| What is on the SIM | one IMSI (host’s range) | one IMSI (sponsor’s range) | several IMSIs plus a switching applet | several complete profiles |
| How switching happens | none; visited network selection only | none | applet rules by country and failure, plus OTA updates | profile enable and disable via remote provisioning |
| Who sets the wholesale rate | host, from its inter-operator tariffs | sponsor, under one contract | each sponsor for its countries; the MVNO picks the cheapest | each operator, per profile |
| Cost profile | highest; little negotiating room | lower in the sponsor’s strong markets | lowest across a footprint; more contracts to manage | depends on each profile’s plan |
| Subscriber experience | one number, one balance | one number, one balance | one balance; number may differ per IMSI | separate numbers and plans unless the MVNO owns all profiles |
| Typical use | domestic brands with occasional travellers | one strong corridor or region | fleets and travellers across many countries | devices that change owner or operator over their life |
The table tells you where each one belongs. Classic roaming is what you get for free. Sponsored roaming fixes one region. Multi-IMSI fixes a footprint. eSIM multi-profile solves a lifecycle problem, not a rate problem.
When an MVNO needs it
Travel is the obvious case, and now a large one. Juniper Research put travel eSIM revenue at 1.8 billion dollars in 2025, up 85 percent year on year (October 2025), and Airalo alone reports 30 million users. Every travel eSIM brand is, in substance, a sponsored-roaming or multi-IMSI operator: it has no network and sells other operators’ roaming footprints, repackaged by destination. An MVNO whose proposition is travel cannot compete on the host’s inherited tariffs.
IoT and M2M fleets are the second case and the more durable one. Kaleido Intelligence estimated 290 million connections managed by IoT MVNOs in 2025, rising to 600 million by 2031 (May 2026). Trackers, meters, payment terminals and vehicles ship from a factory in one country to customers in many, and the customer does not want a different SKU per destination. One multi-IMSI SIM that finds the cheapest network wherever the device lands removes that problem, and the failover rule doubles as a coverage guarantee for devices that cannot be sent back for a SIM swap.
Cross-border communities are the third. The corridors described in our piece on cross-border MVNOs, remittances and Africa involve people who live in one country and have family, income or business in another. A subscription that is at home on both sides of the border, at domestic rates on both sides, is a product a single-IMSI MVNO cannot make.
Enterprise devices round it off. A bank’s payment terminals, a utility’s field tablets, a security firm’s cameras travel less, but they need coverage where the host is weak, and the enterprise wants one contract and one invoice. A domestic second sponsor gives the device a fallback network without a national roaming agreement the MVNO could never sign itself.
Where it does not pay off: a consumer brand in one country whose subscribers take two holidays a year. The extra contracts, SIM cost and settlement work outweigh the roaming margin, and a roaming add-on from the host does the job. Multi-IMSI is for operators whose subscribers or devices are structurally, not occasionally, away from the host.
What it does to billing
This is the part SIM applet vendors talk about least, and where most of the effort lands. Multi-IMSI multiplies the counterparties on the wholesale side while the subscriber still expects one plan and one balance on the retail side. The BSS has to reconcile those two views, and four things follow.
Rating has to work per IMSI and per sponsor. The same gigabyte costs the MVNO a different amount depending on which IMSI carried it and where, so wholesale rating needs a rate card per sponsor per destination, not one per host. Retail rating should be blind to the IMSI: the subscriber bought “5 GB in Europe and North Africa” and the plan should decrement the same way whichever sponsor served the session. The online charging system therefore has to map each usage event from IMSI to ICCID to account before rating it, in real time, against one balance. Avante OCS does this by design, but it is worth confirming with any vendor: ask how a single allowance is decremented from records that arrive under three different IMSIs.
Usage arrives from several networks in several formats at several speeds. One sponsor may offer real-time charging control through a Diameter or CAMEL relay; another delivers TAP files through a clearing house a day or two later, with fraud records a few hours after the event. Mediation has to normalise all of it into one stream. Where a sponsor gives only delayed records, the OCS cannot stop a session when the balance runs out, and the MVNO carries the exposure. Spend caps and hard limits per IMSI are the mitigation, configured per sponsor because the delay differs.
Settlement happens with each sponsor separately. Each sends an invoice built from its own records under its own rate card, to be reconciled against what mediation collected, disputed where they diverge, and paid. An MVNO with four sponsors runs four wholesale relationships that look very much like interconnect settlement, which is why the interconnect and partner-management modules of a BSS are their natural home, and why a platform without those modules ends up doing it in spreadsheets.
Finally, the steering rules become a commercial configuration. Which IMSI to prefer in which country is a cost decision that changes when a sponsor renegotiates, and somebody has to own the loop from the rate cards in the billing system back to the rule table on the card. Operators who treat the applet as a one-off technical set-up leave margin behind every time a sponsor’s price list changes.
Where Avante fits
Avante supplies the BSS an MVNO runs, and multi-IMSI is one of the operating models it was built for. Mediation collects records from the host and from each sponsor, in their own formats and at their own cadence, and attributes them to one subscriber. Avante OCS rates them against a single retail balance in real time where the sponsor allows it, with per-IMSI spend controls where it does not. Interconnect and partner management hold a rate card per sponsor and reconcile each wholesale invoice. VENTAmobile in Latvia runs its sponsored roaming, multi-IMSI, M2M and eSIM business, along with wholesale voice and SMS transit, on the Avante platform. The modules and the interfaces to host and partners are described on the platform page; the vocabulary, including IMSI, ICCID and DSA, is in the MVNO glossary.
Frequently asked questions
What is a multi-IMSI SIM?
A SIM, or an eSIM profile, that stores several subscriber identities from several home operators, together with an applet that chooses which one to present to the network. The choice follows rules loaded on the card, typically by country and by registration failure, and the rules can be updated over the air. To each visited network the device looks like a normal roamer of whichever operator’s IMSI is active.
Is multi-IMSI the same as sponsored roaming?
No, though they usually appear together. Sponsored roaming is a commercial arrangement in which an MVNO uses a partner’s IMSI range and, with it, the partner’s roaming agreements and rates. It works with a single IMSI. Multi-IMSI is the technical mechanism that lets one SIM carry several such sponsor identities and switch between them, so an MVNO can combine several sponsors’ footprints.
Does multi-IMSI need eSIM?
No. It works on a conventional plastic SIM and on an eSIM profile alike; the switching logic lives in an applet inside the profile. eSIM multi-profile is a different technique, in which the eUICC holds several complete operator profiles and switches between them through remote provisioning. That solves lifecycle problems, such as changing operator without a physical swap, rather than roaming cost.
Why is multi-IMSI roaming cheaper?
Because the wholesale rate a device pays abroad is set by the roaming agreement of its home operator, and a specialist sponsor with volume in a given region negotiates a better rate there than a general-purpose host. Multi-IMSI lets the MVNO use the best sponsor in each country rather than one host everywhere. The saving is offset by more wholesale contracts to manage and a more demanding billing set-up.
What does the billing system need to support multi-IMSI?
Mediation that takes records from several sponsors in different formats and delays and maps each one to the subscriber; a rating engine with a wholesale rate card per sponsor and destination but a single retail balance per subscriber; real-time charging where the sponsor offers it and spend controls where it does not; and partner settlement that reconciles each sponsor’s invoice against collected usage.
Which MVNOs should not bother with multi-IMSI?
Domestic consumer brands whose subscribers travel occasionally. For them the host’s roaming add-on covers the need, and the extra sponsor contracts, SIM cost and reconciliation work cost more than the margin they recover. Multi-IMSI pays off when subscribers or devices are away from the host network for a large share of their usage: travel products, IoT fleets, cross-border communities and distributed enterprise devices.