The acronym SIM stands for Subscriber Identity Module. It is sometimes loosely referred to as a smart card but note that the content and relevance of a smart card is often very different to that of a SIM card.

In appearance the SIM is a plastic card with a customised electronic chip that is loaded with a proprietary program to perform security authentication. At this stage, it is called a 'blank card'. The chip is normally visible on one side and this side is known as the 'front of the card' or 'the chip side'. The front of the card also carries the Via Inmarsat logo.

The purpose of a SIM card is to provide a personal identity (PID) to the customer so that he/she is not tied to a single/specific mobile phone (terminal) when making or receiving calls. A SIM card offers a form of 'personal mobility'. Additionally a SIM card comes with features to store mobile numbers (IMNs) and service related information electronically for easy access.

NOTE: When inserted in an Inmarsat-phone, calls made will be charged to the owner of the SIM card. The owner of the terminal where the SIM card was inserted shall not be billed. Storage of a mobile number (IMN) on a SIM does not imply that the SIM is active. Activation is still performed through the service activation system.

Currently SIM Cards are only used for Inmarsat-Phones (Mini-M) and GAN. However, it is possible that SIM cards will be available for future Inmarsat systems.

Who provides, owns and uses SIM card?

• SIM cards are produced by SIM manufacturers (e.g. Gemplus, Orga)
• SIM cards are procured by an individual ISP or a LESO which operates as an ISP according to contract arrangements
• SIM cards are issued to customers by ISPs
• SIM cards are registered by the Customer (or ISP on behalf of the Customer) to a PSA

PID stands for Personal Identity Digit and is used to uniquely identify a SIM card. Keys are used as part of the authentication process to ensure that only valid SIM cards are allowed access. Only authorised ISPs are allowed to request for the PIDs and keys.

PIDs and keys are supplied by Inmarsat directly to the SIM card manufacturer. These are distributed via the Forward and Return Link Pair (FRLP) Bulletin Board which is owned by Inmarsat. Access to the board is limited to SIM card manufacturers only.

PIDs and keys are owned by the ISP and are non-transferrable to another ISP.