Read Answer #5 by Granit > http://lockergnome.net/questions/34129/is-apple-leaving-america-out
It was actually like this out side the US as well. Apple, especially in 2007, is not necessarily the biggest company in the world and even now can't make enough products to keep up with demand and other issues. They started with a small set of markets, with 1 carrier in each, and have slowly expanded from that. Apple started to move on to multiple carriers in some markets because it was illegal to have a set product locked to only one (such as in France).
Apple has a 5 year deal with AT&T that ends in 2012, but it's possible Apple and AT&T could negotiate a new one or cancel the current. I do see the iPhone on other carriers in the future and a person working for T-Mobile USA has reported anonymously that there's an 80% chance they will get the iPhone 4 this fall, as Apple and T-Mobile are in fact in talks right now. There's also strong reports of Verizon getting it in the beginning of 2011, though I can't imagine Apple spending all the time redesigning the iPhone for Verizon's network, when in less than 6 months from then, Apple will come out with a whole new one. If anything Apple would wait til July of 2011 to come to Verizon. Apple and Verizon have been in reoccurring talks since 2006, and was Apple's original choice, however Verizon turned them down.
Jul 21 '10 at 19:31