What Is an International Mobile Subscriber Identity (IMSI)?


Quick definition: IMSI stands for International Mobile Subscriber Identity. It’s a unique number that Mobile Network Operators (MNOs) use to recognize individual subscribers, and it’s a key component of a Subscriber Identity Module (SIM) profile. 

IMSI numbers are usually 15 digits, and they have three distinct parts:

  1. The first set of digits is the Mobile Country Code (MCC), which defines the country a subscriber primarily operates within. This is always either two or three digits.
  2. The second set of digits is the Mobile Network Code (MNC), which identifies the specific MNO a subscriber is associated with. This is between one and three digits.
  3. The final set of digits is the Mobile Subscription Identification Number, which is unique to the subscriber. (This is typically nine or ten digits.)

For example, here’s what you can learn from the IMSI number 310410123456789:

Mobile Country Code


United States

Mobile Network Code



Mobile Subscription Identification Number



An IMSI is not the same as an Integrated Circuit Card Identification (ICCID) number. While they are both parts of the SIM profile, an IMSI identifies the subscriber, whereas the ICCID identifies the SIM card itself. Multiple SIM cards will have the same IMSI if they’re associated with the same subscriber, but they will each have a unique ICCID.

Every cellular-enabled device has an IMSI number stored within its SIM card, and when the device attempts to connect to a mobile network, the MNO uses the IMSI to authenticate it. 

While every IMSI comes from a specific Mobile Network Operator, they allow a device to attach to networks from more than one MNO. Which networks your device can connect to depends on the agreements your MNO has negotiated with other providers. 

Any time a device attaches to a network that doesn’t belong to the subscriber’s primary MNO, the device is considered “roaming,” and the subscriber will pay adjusted rates for any services they use on the network.

Your IMSI has an associated network coverage list that includes your MNO and any Network Roaming Partners they have agreements with.

How IMSI numbers create challenges for IoT manufacturers

There aren’t many situations where an average consumer will want to juggle multiple contracts or SIM cards. So for cell phones, it makes sense to have a single IMSI on a device. But in cellular Internet of Things (IoT), being limited to a single IMSI creates some significant challenges for device manufacturers.

Lack of coverage

The first two parts of every IMSI (the Mobile Country Code and Mobile Network Code) define which network the subscriber will use in a particular country. If you deploy within that country, your devices can only attach to that MNO’s network (AT&T in the example above). In regions where this “home network” has poor coverage, your device may lose connectivity. And your customers won’t blame your provider. They’ll blame you.

If you deploy outside of your home network or your device is mobile and roams often, you’ll have more options—but the networks your device can attach to will be based on your carrier’s list of Network Roaming Partners, not the networks that have the best coverage in your region.

Your connectivity isn’t optimized for the best global coverage. It’s optimized for your MNO’s profit margins.

Network challenges

Relying on a single carrier can put you in a vulnerable position. When they have problems with their infrastructure and experience outages and downtime, that impacts your ability to serve your customers. Their dead zones become your dead zones. If their technology is outdated, your devices suffer. And if they change their prices, you’re stuck paying more for the same coverage.

The IoT solution: Network-agnostic SIM cards

Nearly anywhere you deploy, there are going to be multiple cellular carriers with coverage. As an IoT manufacturer, you want your devices to connect to whichever network has the best signal, and for applications with high data throughput, you want to avoid roaming costs by working with a local operator.

You don’t have to lock yourself into a relationship with a single operator, where you’re beholden to their list of approved roaming partners. With network-agnostic SIM cards, your device can automatically attach to the network with the best signal or lowest costs. Instead of navigating multiple contracts, you can use a single service provider—like emnify.

Maximize global coverage with EMnify

emnify is a complete end-to-end connectivity provider. We build Multi-IMSI SIM cards in all form factors, and when you let us handle your connectivity, your devices can connect to over 540 cellular networks in more than 180 countries right out of the box. 

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