Check Your ICCID, IMEI or IMSI Instantly

Use the free tool below. It parses all three identifiers, validates the Luhn checksum on ICCIDs and IMEIs, and shows you what each segment means. Everything runs client-side in your browser, with no data sent anywhere.

One smartphone on a network carries at least four active identifiers at once, and an IoT device with an eSIM carries more. Most guides explain one number in isolation, so anyone asking “what is the difference between an ICCID and an IMSI” ends up stitching the answer together from four browser tabs. This blog fixes that. It decodes all seven identifiers in one place, shows how they fit together, and gives you a working parser tool to inspect a real ICCID, IMEI or IMSI yourself. It serves two readers: the telecom architect who needs standards-grade definitions, and the device owner who just wants to know which number to read off their phone.

The Seven Cellular Identifiers at a Glance

Before decoding each number, it helps to see them side by side. Every identifier below answers a different question: which card, which subscriber, which device, which network profile, which phone number. They are issued by different bodies and governed by different standards, which is exactly why they are so easy to confuse.

ICCID: The SIM card’s serial number

How an ICCID Is Structured

Read left to right, an ICCID breaks into five parts:

• Major Industry Identifier (MII), digits 1 to 2. Always 89 for telecommunications, which is what tells a system this is a SIM and not a credit card.
• Country code, digits 3 onward. A one to three digit ITU country code for where the card was issued, which is why ICCID length varies slightly by country.
• Issuer Identifier Number, the next two or more digits. Identifies the issuing operator. It is often close to, but not always identical to, the Mobile Network Code.
• Individual Account Identification, the long middle block. The unique serial that distinguishes one card from every other card from the same issuer.
• Luhn check digit, the final digit. A Mod 10 checksum that lets a network instantly catch a transposed or corrupted number.

ITU-T E.118 specifies a maximum of 19 digits, while older GSM specifications allow a 20th digit. Some modem commands also return an extra trailing digit that is not officially part of the ICCID, which is the usual source of the “is my ICCID 19 or 20 digits” confusion. Spenza’s dedicated ICCID guide goes deeper on the encoding and on bulk ICCID extraction for fleets.

IMSI: The subscriber’s network identity.

How an IMSI Is Structured

The IMSI has three parts:

1. Mobile Country Code (MCC), 3 digits. Identifies the subscriber’s home country. The United States uses the 310 to 316 range; India uses 404 and 405.
2. Mobile Network Code (MNC), 2 or 3 digits. Identifies the home operator within that country. The MCC and MNC together point any network in the world to your home operator.
3. Mobile Subscriber Identification Number (MSIN), up to 10 digits. The unique subscriber serial inside that one operator.

The IMSI is deliberately hidden from end users. Because broadcasting it constantly would let anyone track a device, networks assign a temporary identity for over-the-air signaling. On 4G and 5G this is the GUTI, and 5G adds concealment so the permanent IMSI is never sent in the clear. This is the open gap in most identifier content: it is the identifier that actually authenticates every call and message, yet it is the least explained.

For IoT fleets, the IMSI is where multi-IMSI and eUICC strategies live. A single eSIM can hold multiple profiles, each with its own IMSI, which is how a device switches home networks for better roaming economics. Spenza covers this in the multi-IMSI versus eUICC guide.

IMEI: The Device’s Unique Hardware Identifier

How an IMEI Is Structured

The 15 digits split into three blocks:

1. Type Allocation Code (TAC), 8 digits. Identifies the make and model. Allocated through the GSMA. More on this in the TAC section below.
2. Serial Number (SNR), 6 digits. Uniquely identifies one device among all devices that share the same TAC.
3. Check Digit, 1 digit. A Luhn checksum over the first 14 digits.

There is a related variant, the IMEISV, which is 16 digits long: the first 14 digits of the IMEI plus a two-digit Software Version Number. The IMEI you dial up with *#06# is the 15-digit form. Changing an IMEI to disguise a device is illegal in most jurisdictions, which is a useful contrast for the comparison section: you can legally swap the SIM, but not the IMEI.

EID and EUICCID: The eSIM Identifier

Why the EID Matters in 2026

A traditional SIM has exactly one ICCID. An eUICC can hold many network profiles, each with its own ICCID and IMSI, and switch between them over the air. The EID identifies the chip that holds all of them. That is the single most common point of confusion: people assume the EID and ICCID are interchangeable, when in fact one identifies the durable hardware and the other identifies a profile that can be added, swapped or deleted.

This distinction became urgent with GSMA SGP.32, the IoT-focused remote provisioning standard that moved into commercial rollout through late 2025 and 2026. SGP.32 lets constrained IoT devices manage profiles without the heavy infrastructure the older consumer standard required. If you are evaluating it, Spenza’s SGP.32 explainer and the SGP.22 versus SGP.32 comparison break down what changed and who should care.

MSISDN: The Public Phone Number

How an MSISDN Is Structured

Under ITU-T E.164, an MSISDN is built from three parts:

1. Country Code, 1 to 3 digits. For example 1 for North America, 44 for the United Kingdom, 91 for India.
2. National Destination Code. Routes to a region or network inside the country.
3. Subscriber Number. The unique line within that destination.

The MSISDN is the most flexible identifier of the seven. It can change while the subscriber stays the same, which is what number porting does. A single IMSI can also have more than one MSISDN attached, for example a voice line and a separate data line. This is why the MSISDN is never a reliable way to identify hardware: it floats above the SIM and the device entirely.

TAC: The Type Allocation Code

The TAC is small but powerful. Because it maps an IMEI to a specific device model, it drives device-type analytics, fraud detection and regulatory reporting. A network can look at the TAC alone and know whether a connecting device is a phone, a tracker, a router or an industrial module, without any other information. The GSMA maintains the official TAC allocation database, and the GSMA’s IMEI and TAC resources are the authoritative reference for how codes are issued.

For an IoT operator running mixed hardware, TAC-level visibility is the difference between “40,000 devices online” and “32,000 trackers, 6,000 routers and 2,000 unknown modules, three of which should not be on this network at all”.

ICCID vs IMSI vs IMEI vs MSISDN: The Big Comparison

Here is the question every other page dodges. If one phone has four identifiers active at once, which one is which? The table below is the fast answer.

Why One Device Carries Four Numbers at Once

Think of a single connected device. The IMEI is the chassis. The ICCID is the SIM slotted into it. The IMSI is the subscription that SIM carries. The MSISDN is the phone number routed to that subscription. Swap the SIM and the ICCID and IMSI change while the IMEI stays. Port the number and the MSISDN changes while the IMSI stays. Each layer moves independently, which is the whole point of the design.

How to Find Each Identifier on Your Device

The fastest universal method works on most phones: open the dialer and enter *#06#. Many devices will display the IMEI, and often the ICCID, EID and MSISDN, on a single screen. The table below covers the menu paths when you need a specific number.

The modem AT commands matter most at fleet scale. They are what let a provisioning system pull identifiers from thousands of devices programmatically instead of someone reading numbers off screens. A practical habit for hardware teams: photograph every SIM with the ICCID visible before installation, because once the card is seated in a sealed enclosure, that number is hard to recover.

Identifiers in the eSIM Era

eSIM does not add a new identifier so much as it rearranges the existing ones. On a physical SIM, the ICCID, IMSI and the card are effectively locked together. On an eUICC, they come apart.

• The EID is per chip. One device, one eUICC, one permanent EID.
• The ICCID is per profile. A single eUICC can hold several profiles, each with its own ICCID.
• The IMSI is per profile too. Each profile carries its own subscriber identity, so switching profiles switches the active IMSI.

So a single eUICC might hold three profiles from three operators, which means three ICCIDs and three IMSIs behind one EID. The device activates one at a time. For consumer phones this enables clean carrier switching. For IoT, under SGP.32, it lets a device be manufactured once and provisioned for whatever market it ships to, which removes the largest logistics headache in connected hardware. If you are sourcing connectivity for this model, Spenza’s roundup of IoT eSIM providers is a useful starting point, and the SIM versus eSIM breakdown covers the tradeoffs.

Security and Privacy: Identifier Risks in 2026

Each identifier is also an attack surface. Knowing which one is exposed in which scenario is basic operational hygiene for anyone managing connectivity.

The practical defenses are not exotic. For consumers: add a carrier-level port-out PIN to blunt SIM swaps, and prefer app-based authentication over SMS codes. For fleet operators: monitor for IMEI and IMSI mismatches, because a SIM that appears in a different device model than its TAC history suggests is worth investigating. Modern 5G networks help by concealing the permanent IMSI and using rotating temporary identifiers over the air.

Identifiers in IoT Fleet Management

Managing identifiers for one phone is trivial. Managing them for a fleet of 100,000 devices is a systems problem, and it is where the difference between identifier types stops being academic. At fleet scale you are reconciling ICCIDs against IMSIs against EIDs across an inventory that changes constantly as profiles are provisioned and devices are swapped. You are using TAC data to audit what hardware is actually on the network, and switching IMSIs to optimize roaming cost per region. None of that works from a spreadsheet. It needs a platform that treats identifiers as first-class, queryable objects.

Bookmark This as Your Identifier Reference

Seven identifiers, seven jobs. The ICCID is the SIM, the IMSI is the subscriber, the IMEI is the device, the EID is the eSIM chip, the MSISDN is the phone number, the TAC is the device model, and the EUICCID is the eUICC serial. Once you can see that hardware identifiers stay fixed while profile identifiers move, every cross-identifier question answers itself.

If you manage connectivity at any real scale, the next step is not memorizing formats, it is putting identifier data into one system you can actually query and act on.

FAQs

Spenza gives device makers, MVNOs, and IoT operators one platform to provision, track, and switch SIM and eSIM identifiers across 180+ countries. Talk to the Spenza team today.