Aside from the world supposedly ending in 2012, that"s the same time the exclusive contract between AT&T and Apple is due to end over the iPhone. Apple and AT&T locked in an exclusive contract back in 2007, when the first iPhone launched.
A California class-action lawsuit filed back in 2007 says that Apple and AT&T illegally exerted a monopoly over the iPhone, requiring customers be locked into a 2-year contact, when the exclusivity deal between Apple and AT&T was actually five years.
This forces customers to resign with AT&T after their contract was up, rather than allowing them to switch carriers - if they wanted to keep using the iPhone.
From these selective quotes from engadget via Apple:
"The duration of the exclusive Apple-[AT&T] agreement was not "secret" either. The [plaintiff] quotes a May 21, 2007 USA Today article - published over a month before the iPhone"s release - stating, "AT&T has exclusive U.S. distribution rights for five years-an eternity in the go-go cellphone world."
...
"[T]here was widespread disclosure of [AT&T"s] five-year exclusivity and no suggestion by Apple or anyone else that iPhones would become unlocked after two years... Moreover, it is sheer speculation - and illogical - that failing to disclose the five-year exclusivity term would produce monopoly power..."
The question remains if the deal between Apple and AT&T is still valid. The lawsuit is still on-going, and Apple has a hit on their hands, something that is limited to the worst ranked carrier in the United States. AT&T still has yet to enable tethering for the iPhone. Many customers still eagerly waiting for Verizon to carry the iPhone in the US, which could happen if the rumours of a CDMA iPhone 4G/HD are true.
The United States is one of very few places around the world that still has an exclusivity deal over the iPhone. Countries like Canada and United Kingdom already allow for multi-carriers, but the United States remains locked down.