Just saying if I bought a phone off Craigslist "which i'd never do" and it got blocked, I would take the first opportunity I had to unblock it.
Yeah I know I'd be such a bastard for being a victim and having my money stolen from me, then changing a number and making everything fine.
The one paying for these types of things should be the carriers not random people looking to get a phone and use their service. Find a new way to deal with it. Carries would most likely even benefit from accepting more customers.