SIM cards store network-specific information used to authenticate and identify subscribers on the network. The most important of these are the ICCID, IMSI, Authentication Key (Ki), Local Area Identity (LAI) and Operator-Specific Emergency Number. The SIM also stores other carrier-specific data such as the SMSC (Short Message Service Center) number, Service Provider Name (SPN), Service Dialing Numbers (SDN), Advice-Of-Charge parameters and Value Added Service (VAS) applications. (look to GSM 11.11).
Each SIM is internationally identified by its integrated circuit card identifier (ICCID). ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalization. The ICCID is defined by the ITU-T recommendation E.118 as thePrimary Account Number. Its layout is based on ISO/IEC 7812. According to E.118, the number is up to 19 digits long, including a single check digit calculated using the Luhn algorithm. However, the GSM Phase 1 defined the ICCID length as 10 octets with operator-specific structure.
The number is composed of the following subparts:
Issuer identification number (IIN)
Maximum of seven digits:
§ Major industry identifier (MII), 2 fixed digits, 89 for telecommunication purposes.
§ Country code, 1-3 digits, as defined by ITU-T recommendation E.164.
§ Issuer identifier, 1-4 digits.
Individual account identification
§ Individual account identification number. Its length is variable but every number under one IIN will have the same length.
§ Single digit calculated from the other digits using the Luhn algorithm.
With the GSM Phase 1 specification using 10 octets into which ICCID is stored as packed BCD, the data field has room for 20 digits with hexadecimal 'F' being used as filler when necessary.
In practice, this means that on GSM SIM cards there are 20-digit (19+1) and 19-digit (18+1) ICCIDs in use, depending upon the issuer. However, a single issuer always uses the same size for its ICCIDs.
To confuse matters more, SIM factories seem to have varying ways of delivering electronic copy of SIM personalization datasets. Some datasets are without the ICCID checksum digit, others are with the digit.