Seth Weintraub over at 9to5Mac heard from a T-Mobile USA spokesman that their network is already home to over 1 million iPhones, and this is without the benefit of an Apple contract, T-Mobile supplied micro-SIMs, or support for their AWS 3G/4G bands. That means, right now, there are over a million people willing to jailbreak and unlock, or buy an unlocked model, manually cut their SIM cards, and go 2G EDGE only just to be on T-Mo with their iPhones.
There have been rumors that iPhone 5 would support T-Mobile's AWS HSPA and HSPA+ bands, and AT&T is trying to buy T-Mobile and if that goes through, it probably means iPhones for everyone.