Apple are tipped to be attempting to further marginalize their carrier partners by using a new pre-programmed SIM card for the iPhone. The card - which according to GigaOm's sources is being developed with Gemalto - has both a pre-written ROM and an upgradable flash chip, the latter capable of being injected with carrier information over a network connection, such as while being activated through iTunes, and would be integrated into the iPhone rather than user-accessible. Gemalto, meanwhile, would handle the backend required for the system.
The programmable SIM would mean iPhone buyers could choose their carrier at the point of sale - either Apple stores or via Apple's online portal - or even through an App Store download, with the latest settings automatically sent to their device and minimal to zero contact with the carriers themselves. Europe is tipped as the most likely market for Apple to debut the system, as the iPhone 4 is currently being sold on multiple networks in various European countries.
The upside for consumers would be an easier setup procedure and potentially more straightforward international roaming. On the downside, by integrating the new SIM into the iPhone's mainboard, Apple would effectively bypass those who currently unlock their handset and swap SIMs at will; you would only be able to change to carriers Apple had "approved" for inclusion in its list of options.
Interestingly, Gemalto are also specialists in NFC and contactless payments, and it's speculated that this play could in fact be the first stage of an NFC-equipped iPhone model. Apple already have multiple patents covering cashless purchasing and related technologies, and this hardware and backend system could easily be turned to implementing those.