Ever since the iphone 3G, I’ve been upgrading every year. In doing so, I always had another phone that was off cycle in that it was now eligible for a “free” upgrade. And I’ve always been on a 2 year contract.
For example, this year I upgraded from my iP5S. When it came, I trotted down to my ATT store where they swapped the sim card from the new phone which has my secondary number into my new IP7, thus changing the number of the new phone.
At the same time, I sold my previous IP6 S, ever though it still had another year to go on the contract. As I said, I’ve done this with the 3G, 3gS, iP4, iP4S, ip5, ip5S, ip6 and this year, the ip6S. Every one of these phones were sold with a year to go on the contract, using my alternating procedure.
I’ve alway put the phones back to factory setting before selling them with the sim card removed. My new phone is the first one that I’ve paid full price for upfront and thus, unlocked.
None of the previous phones I’ve sold were unlocked and technically had a year to go on the contract. I’ve never heard a peep about the phones I’ve sold so I don’t understand this thread and why the OP is having trouble using the phone he bought from craigslist. Don't know if it makes a difference, but all phones were ATT.