Which is true. If you really want "freedom" for your mobile, you have to bite it, get a foreign unlocked phone. I got phones here where I can easily remove the SIM of one carrier to another if I am not happy. BTW, smartphones for Latin America and Australia do use the same 850 band as AT&T. But you don't get the warranty and they may switch you to a smartphone contract.
The lock in system, you buy a contract phone, you are locked in for two years, is inherently uncompetitive because it does not force carriers to improve their act. Three years of iPhone dominance, and has AT&T improved any better than its competitors? There is a survey that suggests at least 22% of iPhone users in AT&T may jump ship to Verizon if there is a Verizon iPhone. That is not what you call happy customers.
But whether Android, iPhone, Windows Phone, no OS platform can solve the messed up situation on the US telecom industry. (Don't believe the crap that iPhone Messianists tells you that Steve Jobs can save you from the tyranny of the US carriers). It takes direct legislation---which is what is actually done in many countries---to create a mobile telecom system that is equitably competitive. Carriers in different countries put the ones in the US to shame and one of the reasons for that is pure competition from prepaid unlocked phones. If your phone is unlocked, you don't like your carrier service, switching to a new carrier is only the cost of a new SIM, not a phone.