What is stored on your SIM card? Some phone numbers, perhaps a few text messages. It also holds security information to identify your handset to the network, a list of preferred roaming partners to access when travelling abroad, a pre-paid top-up mechanism and other basic operator services.

The SIM has always been your identity token: out of sight and out of mind most of the time, but serving to authenticate you to the network and allowing you to move key parts of your mobile experience (e.g. your own phone number and your contacts) to a new handset.

It forms an important part of your relationship with the operator. Indeed, it is one of the first things operators started applying their brand to, long before handsets started appearing with the operator logo alongside that of the handset manufacturer.

SIM card providers such as Gemplus (now part of Gemalto – a merger with Axalto), Oberthur and Giesecke and Devrient (G&D) have been trying to leverage their unique position as suppliers of this ubiquitous component for some time. They’ve developed SIM Toolkit for building operator services into their cards, collaborated closely on standardisation and embedded Java for more advanced applications.

Now they’re trying to further enhance their offering by significantly expanding the memory capacity of their cards. Orange and Oberthur, working in partnership with M-Systems, have recently unveiled the first handsets for the UK market with 512 Mb SIM cards, following a deal agreed in February. Users will be able to store Java applications, music and videos on the cards, all secured with DRM and portable if they upgrade to a new handset in the future.

Orange is deploying these throughout its European operations.

There are several advantages to operators using large capacity SIMs over other memory card options. Most obviously, it reduces the supply cost and complexity by centralising everything in one unit. The SIM also features built-in security capabilities to ensure content is protected.

However, the SIM card vendors ambitions do not end there. Gemplus, for instance, is marketing a solution known as .SIM (dotSIM), which provides operators with a server-based management system for remotely updating the SIM, adding new services and extending the operator’s reach into other environments – such as fixed broadband.

In this PDF, Gemplus explains its vision of the mobile number (and by association, the SIM card) as the universal identifier for a subscriber across cellular, VoIP and other interactive services. It describes how the SIM can be used to customise the handset interface and host an on-device portal for browsing content off-line. Services can be remotely managed and updated by the operator directly on the SIM card.

G&D paints a similar vision of a SIM-based future in this white paper, which also includes a comprehensive explanation of SIM architecture.

This is potentially a very attractive model for operators. The SIM has several advantages: it is ubiquitous, there is already a competitive market among suppliers, it is manageable, low cost and closely tied to the operator’s brand. It can also be easily secured and blocked if lost. With capacities of 1 Gb already available, it would seem an ideal vehicle for storing all the elements which comprise a user’s mobile identity and multimedia gallery.

For operators, it could be the easiest way to shift primacy of the consumer brand relationship from the hardware manufacturer to the service provider.

There is also clear benefit to the user. They have a physical and portable token for storing their information, which can be used to easily upgrade or switch devices. This will require the operator to find a way of backing-up the information held on the SIM so it can be easily restored if the card itself is lost by the subscriber.

If SIM cards do emerge as a mechanism for advanced service delivery and content storage, there is a wider implication: it will further centralise control of the experience with operators, making it more difficult for third party content providers to manage the relationship with their customers.