This does not mean that a phone containing this SIM card can connect to a maximum of only 33 or 80 networks, but it means that the SIM card issuer can specify only up to that number of preferred networks.
If a SIM is outside these preferred networks it uses the first or best available network.
Modern SIM cards allow applications to load when the SIM is in use by the subscriber.
These applications communicate with the handset or a server using SIM application toolkit, which was initially specified by 3GPP in TS 11.14.
The ICCID is defined by the ITU-T recommendation E.118 as the Primary Account Number.
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 digit "F" being used as filler when necessary.
However, a single issuer always uses the same size for its ICCIDs.
(There is an identical ETSI specification with different numbering.) ETSI and 3GPP maintain the SIM specifications.
The main specifications are: ETSI TS 102 223, ETSI TS 102 241, ETSI TS 102 588, and ETSI TS 131 111.
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 personalisation.