Moving from regular SIMs to micro SIMs for the iPad and iPhone 4 was a fairly user-hostile move on Apple's part, seeing how it made moving between an iPhone and virtually any other GSM device quite a bit more difficult; the official explanation (for the iPhone 4, anyway) was that there simply wasn't room for a regular SIM, but that seems unlikely considering that you're only saving 10mm of length, 3mm of width, and 0mm of thickness. A more plausible scenario is that Apple viewed micro SIMs as a way to get ahead of the industry curve a bit and make it unpleasant for users to try to share an iPhone line with other devices, a concept that gets at the core of Apple's mantra of owning the entire ecosystem from end to end.
But could they be trying to take that concept another step further? GigaOM is reporting a rumor today that Apple is working tightly with security firm Gemalto -- you know, the SIM guys -- to integrate software-reconfigurable SIMs right into European iPhones that would be activated on the carrier of your choice using an App Store download. Why European models? Multiple carriers offer the iPhone in a number of European countries, so distribution is a bit more complicated there than it is in the US, though it's a reasonable leap to suggest that the same integrated SIMs would be use on new North American iPhones as well. From Apple's perspective, it's a win-win: trying to use your iPhone line with another device would be akin to pulling teeth, and more importantly, Apple wouldn't need to worry about bundling carrier-specific SIMs with devices. In fact, the move would make Apple's (and the consumer's) interactions with the carrier entirely virtual, all the way from manufacture to activation. Seems like the plan would require an extraordinary amount of buy-in from carriers who've become increasingly suspicious of Apple's goals lately -- but then again, they managed to get carriers to suddenly and rapidly deploy micro SIMs en masse, and if anyone could pull this off, it'd be Steve's boys and girls.