Apple could be developing a built-in SIM card for thethat would allow European users to switch networks without having to swap SIMs.
According to GigaOM's sources inside European carriers, Apple is working on the project with SIM-card manufacturer Gemalto. Apparently, the aim is to reduce the role of operators in the process of purchasing and using an iPhone.
You'd be able to buy an iPhone from Apple's website or retail stores and decide at the same time which carrier you wanted to use. Alternatively, you could buy an iPhone and set it up with a carrier through a download in the App Store, rather than interacting with the carrier directly.
Once your iPhone is set up, you'd be able to change network, using an app or iTunes, to take advantage of a better deal, without needing to swap carrier-specific SIM cards.
Ultimately, you'd still be in thrall to the operators, as you'd still need to pay them to use their networks. But being able to swap between networks so easily might force operators to become more competitive and result in better deals.
Also, if you wanted to take your iPhone out of the country, you wouldn't need to swap SIM cards to change networks, as it could all be done through the handset. Once overseas you could use a local network, which would prove much cheaper than paying international roaming costs. You'd be able to use data-intensive applications without worrying about how much it will cost.