I'm surprised some dinosaur carriers in the US still lock their phones. In Europe it hardly happens anymore. I also don't see the added value for carriers. In the modern day, carriers are not able to differentiate by phones anymore (every carrier has the same Galaxy and iPhone), so all they are really doing is generating unhappy customers. It also costs them a lot of trouble.
I don't understand it.
It is a slow transition in US. People here don't know how to pay $800 for iPhone. But they can understand paying $200 and signing 2 year contract. In the end they will pay more but it is still easier than upfront bill.