Why would AT&T care of you swap in another sim if they have you on a two year contract anyways?
This question hints at the core for the whole thread: Why would a company do something if there was no incentive, if there was no advantage to locking your phone? If I'm Verizon and you bought a phone from me and at one, two or three years, you got another phone. Would I care if the first phone had to be used on a Verizon network? Sure I would - cause the guy who bought it from you couldn't then use the phone with my competitor. Locking is a way of marking territory, of making sure the % of devices sold for a given carrier for a give year, stay with that carrier.
Smart regulations foster a better marketplace for business and customers alike.
I've enjoyed many of the posts in this thread, from both 'sides'. It seems like everyone agrees that competition and choice is good. There's just a difference is how that can best be ensured. But both can be good and both can be bad. As a business can grow to powerful and stifle a market (less competition), so to can a government. I would go far as to say that only when both business and government are in play and working in balance, is maximum competition possible.