I wonder how this will work with used phones purchased privately. I bought a phone on craigslist that was locked to T-Mobile. It wasn't blacklisted so I'm able to use it on T-Mobile, but I don't know if the contract was paid in full, the original account is in good standing, etc.
I think, because, the contract is between you and the carrier you should be okay. Even if you sell your phone to someone else you're still obligated to pay your bill or terminate early.
Carriers aren't stupid. They sell you a phone at a quarter of the price because you will pay nearly if not more than $100/mo. and they have recouped their loss by the end of April.
