ICCID and IMSI decoder

What the numbers mean

• ICCID (Integrated Circuit Card Identifier) is the serial number of the SIM itself, printed on the card. It starts with 89 for telecoms, then the issuer's country calling code (44 for the UK), then the issuer's identifier and the card's own number, and ends with a Luhn check digit. It identifies who made and issued the card, which for an IoT SIM is often not the network it roams on.
• IMSI (International Mobile Subscriber Identity) is the identity the SIM presents to the network. It starts with the mobile country code (MCC, 234 or 235 for the UK) and the mobile network code (MNC, two or three digits), followed by the subscriber's own number. A multi-network IoT SIM may carry several IMSIs and switch between them.

Issuer and network names come from the official ITU lists, updated with Ofcom's current list of UK network codes, and with brand names from Wikipedia. Some issuer names are historical; where we know the current owner, the decoder shows it.

Sources: ITU-T E.212 list of Mobile Network Codes and E.118 list of Issuer Identifier Numbers, © ITU; Ofcom UK Mobile Network Code list, Ofcom copyright; Wikipedia, Mobile country code. The decoder's data (mcc-mnc.json, iccid-issuers.json) is available under CC BY-SA 4.0.