Difference between IMEI, IMSI, ICCID and MSISDN numbers

The number of connected mobile devices is growing at a rapid pace and the new 5G technology will only accelerate it. We have more than 8 billion mobile subscriptions already in the world and now with the growth of the Cellular Internet of Things (CIoT), we can expect an even larger number of connected cellular devices. As more devices join the network, device identification becomes increasingly important in a world where device manufacturers are continuously evolving identification methodologies. Accurate identification of mobile devices is vital for mobile network operators for assigning the right services to the right devices. Mobile networks use various unique codes to be able to dispatch the services relevant to specific subscribers accurately. IMEI, IMSI, ICCID and MSISDN are some of the key codes required for the identification of mobile devices.

IMEI is a 15 digit number assigned to every cellular device for each of its SIM slots; IMSI is a 15 digit number assigned to the SIM of a mobile subscriber; ICCID is a number that identifies the chip of each SIM card; MSISDN is the full mobile number including the country code and any prefixes.

So basically, the IMEI number is linked to the mobile device (e.g. your smartphone) whereas IMSI, ICCID and MSISDN are linked to the subscriber or SIM (Subscriber Identity Module). These concepts work the same way if you are using a regular plastic SIM or an embedded SIM (eSIM) eSIM.

What IMEI stands for and what it means

IMEI stands for International Mobile Equipment Identity, and it is a unique fifteen digit number assigned to every cellular device for each of its SIM slots. Cellular devices like smartphones are SIM-enabled which means you have to put in a SIM card to connect them to the network. We have multiple SIM options in newer mobile phones, including a physical compartment for slotting in a plastic SIM and an embedded SIM called eSIM inside the phone that you can manually assign to a mobile network. The IMEI number is unique to every cellular connection; therefore, if you have a dual-SIM phone (a phone that can take two SIMs), whether plastic or electronic, your phone will have two IMEI numbers. International Mobile Equipment Identity can be assigned to every mobile cellular device including (but not limited to) mobile phones and mobile broadband data cards. It is programmed into the mobile device by the device manufacturer. The IMEI number stays with the mobile device over its lifetime and must not be modified. Only the manufacturers of the mobile device are allowed to assign this number. The act of changing this number is called “unblocking” which is a criminal offence under UK laws.

What does an IMEI number look like?

The IMEI number is a 15 digit code, all numeric, which shows up on all mobile phones in the same number format. However, the user interface (UI) design may differ depending on the device manufacturer and operating system. Below are some pictures to show you exactly what the IMEI number looks like on smartphones.

what is imei number
Example: IMEI number displayed on a Huawei Android phone (We have updated the screenshot to replace the actual IMEI)
Example of how IMEI is displayed on an iPhone (We have updated the screenshot to replace the actual IMEI)
Example of how IMEI is displayed on an iPhone (We have updated the screenshot to replace the actual IMEI)
Example: IMEI number displayed on an old Samsung Android phone (We have updated the screenshot to replace the actual IMEI)
Example: IMEI number displayed on an old Samsung Android phone (We have updated the screenshot to replace the actual IMEI)

What is the IMEI number used for?

The IMEI number is a unique device identifier that lets mobile operators know which device is trying to access the mobile network. Unlike IMSI (International Mobile Subscriber Identity), which is a SIM-specific identifier, IMEI is unique to the device itself. If a mobile phone gets lost or stolen, the IMEI number is the way to block the handset from being misused. As a mobile phone user, if you lose your phone for whatever reason, you need to ensure that you contact your mobile operator to block the IMEI and IMSI because IMEI is specific to your device, and IMSI is specific to your SIM. IMEI number allows an operator to place a specific mobile phone on a blacklist which means the phone is prohibited from accessing the mobile network no matter which SIM is inside it. The device registration and tracking capability reside within the mobile core network. Equipment Identity Register (EIR) is the entity within the mobile core network that stores the IMEI information in a database.

How can I check my IMEI number?

There are multiple ways of checking IMEI numbers. The quickest way to check your IMEI number is to type a sequence *#06# on the dial-pad of your cell phone, which will display the IMEI number on the phone screen. You can also check the IMEI number by going into the ‘Settings’ menu on your phone. For iPhones, you need to go to “Settings”–> “General” –> “About” and then scroll down to find your IMEI number. For Android phones, generally, you can go to “Settings”–>”About phone” to find the IMEI number. You can also check the IMEI number on other devices like SIM-enabled tablets, smartwatches and cellular mobile broadband routers. Check out this dedicated post to learn some ways of checking the IMEI number on your cellular devices.

What is IMSI (International Mobile Subscriber Identity)?

International Mobile Subscriber Identity or IMSI is a unique number assigned to the SIM card of a mobile subscriber. IMSI is usually a 15 digit number that identifies the mobile user within the mobile network. In order to ensure the confidentiality of the mobile user, the network uses a temporary number known as TMSI (Temporary Mobile Subscriber Identity) during most of the communication with the mobile phone.

IMSI is usually a 15 digit number where the first three digits represent the Mobile Country Code (e.g. 234 for the UK), the next two digits represent the Mobile Network Code (e.g. 15 for Vodafone UK), and the last ten digits represent the Mobile Subscriber Identification Number. The Mobile Subscriber Identification number is the identity of the subscriber within the Public Land Mobile Network (PLMN). IMSI is used whenever the mobile phone tries to access the mobile network irrespective of which technology it is using i.e. 2G GSM, 3G UMTS, 4G LTE or 5G NR.

As mentioned above also, the mobile network may use a temporary IMSI called TMSI (Temporary Mobile Subscriber Identity) instead of IMSI to ensure subscriber’s confidentiality. A user does not need to know or worry about their IMSI number, however, they can use available apps in app stores to be able to find out their IMSI number. Mobile operators use IMSI as the identity of the mobile subscriber to assign and manage any services allocated to that particular subscriber. As an example, the first two parts of the IMSI number i.e. Mobile Country Code and Mobile Network Code can indicate when a mobile user is outside of the country and roaming which can, in turn, allow mobile operators to apply the correct billing.

What about ICCID and MSISDN?

When we talk about IMSI and IMEI, we often also come across other inter-related codes that may be a bit confusing. The ‘usual suspects’ are ICCID and MSISDN, so let’s clarify them:

  • ICCID: ICCID stands for Integrated Circuit Card Identifier and it is a number that identifies the chip of your SIM card (the shiny golden part of the SIM). In other words, it is the identity given to the your SIM card (physical/plastic SIM or embedded SIM), irrespective of what your mobile phone number is. As you may know, you can get any SIM card (chip) from your mobile operator and get them to reassign the mobile number to that SIM. That’s why ICCID is important as it keeps track of the chip of your SIM or eSIM. ICCID number is stored in the SIM card but it is also printed on the SIM (long number with around 20 characters).
  • MSISDN: MSISDN stands for Mobile Station International Subscriber Directory Number and it is actually a lot simpler than it sounds. It is your full mobile number including the country code and any prefixes (if applicable). For example, in the UK, the country code is +44 (or 0044) and the mobile numbers start with 07. When you write the MSISDN, you take away the + sign (or 00), and you take away ‘0’ from 07 to get something like this: 447xxxxxxxxx.
Example of ICCID and IMSI numbers


IMEI and IMSI are two unique codes used for the identification of a mobile user. IMEI stands for International Mobile Equipment Identity and it is a unique number assigned to every mobile device including mobile phones, dongles, cellular IoT sensors, data cards etc. IMSI stands for International Mobile Subscriber Identity and it is a unique number assigned to the SIM card used by the mobile device.

Here are some helpful downloads

Thank you for reading this post, I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need some extra support, especially when preparing for a new job, studying a new topic, or maybe just buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.

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