ICCID, IMSI, and IMEI
Quick definition
ICCID identifies the physical SIM chip. IMSI identifies the subscriber on the mobile network. IMEI identifies the device (modem) holding the SIM. Three different identifiers, all three needed to manage an IoT fleet.
ICCID: the number on the plastic
Printed on the SIM, 19-20 digits. Used to locate the SIM in the carrier portal, activate it, top up. Follows the ITU-T E.118 numbering plan.
IMSI: the network identity
Assigned by the carrier, stored inside the SIM (not printed). What the carrier authenticates. A eUICC or Multi-IMSI SIM may hold several IMSIs.
IMEI: the hardware identity
15 digits, assigned to the modem at the factory. Does not change when you swap the SIM. Useful to detect swaps, bind SIM to hardware, or block stolen units.
FAQ
Why register the IMEI?+
To bind SIM and device. If the SIM moves to a different IMEI you get an alert. Useful against fraud and fleet theft.
Where do I find the IMSI?+
Usually in the carrier portal or via API. It is not printed on the SIM (unlike the ICCID).
Related terms
What is MFF2
MFF2 (Machine-to-Machine Form Factor 2) is the solderable SIM: a 6x5 mm chip mounted directly on the PCB, no tray or socket. It is the de-facto standard in industrial IoT, automotive, and any device facing vibration, humidity, or extreme temperatures.
What is Multi-IMSI
Multi-IMSI is a SIM technology that hosts several IMSIs (subscriber identifiers) on a single card and picks one based on country, signal quality, or cost. The device authenticates as a customer of carrier A in one place and as carrier B in another, with no hardware change.
What is eUICC
An eUICC (embedded Universal Integrated Circuit Card) is a programmable SIM chip that can hold several carrier profiles and switch between them over the air. It is the GSMA standard underpinning every modern eSIM, in phones, vehicles, and IoT devices.