If you're picking a SIM technology for an IoT deployment, you'll hit two acronyms: Multi-IMSI and eUICC. Both let a single SIM card use multiple mobile operators. The difference is when the operator is selected, and that has real consequences for cost, complexity, and how you manage the fleet over its lifetime.

What's an IMSI?

An IMSI (International Mobile Subscriber Identity) is the unique 15-digit number that identifies a SIM to the mobile network. Every SIM has at least one IMSI; it's how the network knows who you are and which operator you belong to.

The IMSI's first few digits identify the home operator (MCC + MNC). The rest uniquely identifies the subscriber. When a device powers on, it sends its IMSI to the nearest cell tower in an "attach" procedure, the network checks whether the IMSI's home operator has a roaming agreement with it, and if so, lets the device connect.

Multi-IMSI: multiple identities, automatic switching

A Multi-IMSI SIM stores several IMSIs on the card itself, typically one per region or operator family. The device scans and selects a network; the SIM presents whichever of its identities is valid on that network. If the attach fails, the SIM can try another identity.

You don't notice the switch as a user. The SIM acts like a regular SIM; it just happens to have a deeper bench of operators it can pose as.

Why this matters:

• Better coverage. No single operator has roaming deals with every network worldwide. Multi-IMSI gives you access to all the networks all the operators in your IMSI pool can reach.

• National roaming. A regular consumer SIM is locked to one home network, even if a competitor has better coverage in your exact location, you can't use it. Multi-IMSI bypasses that lock.

• Better rates. Different operators have different commercial deals in different countries. Multi-IMSI can pick whichever has the best rate for the country you're in.

• One SIM, global deployment. No need to ship different SIMs to different markets. The same Multi-IMSI SIM ships everywhere and figures it out on attach.

eUICC: one profile at a time, swappable over the air

An eUICC (embedded Universal Integrated Circuit Card) holds operator profiles that can be downloaded, activated, and replaced remotely, without anyone touching the SIM. Only one profile is active at a time, but you can change which one over the air via the SM-DP+ provisioning system.

eUICC chips can be embedded in the device (no removable SIM tray) or come on a removable card. The chip is what makes OTA possible; the form factor is independent.

Why this matters:

• Remote provisioning. Change operators after the device is deployed, useful for fleets where you need to switch carriers in response to a price change, an outage, or a market entry.

• Regional optimisation. Each profile is purpose-built for a region. Once installed, the SIM works as if it were a native local SIM, with no roaming overhead.

• Future-proofing. New operators can be added years after manufacture by pushing a new profile.

• Pre-provisioning at the factory. Manufacture the device once, then load the right profile when the customer activates it.

Side-by-side

Simbase profiles by technology and ICCID range

Simbase uses Multi-IMSI and eUICC technologies across its profile range, plus Single-IMSI for the simpler regional profiles:

Common questions

Related

• eSIM, what it is and when to use one

• SIM Profiles, overview of the SIM profiles Simbase uses

• Configure the Simbase APN on your device, APN values differ by profile