AT&T says they will give you a large "trade-in" for your old phone.

Hidden in the fine print is the detail that you will receive the trade-in in small payments over 36 months. If it anytime you cancel your phone plan you lose the remaining "trade-in" payments.

When speaking with one of their representatives, they admitted that this is a way of getting you to stay with them for three years. It's basically a way of tricking you into behaving as though you have a contract. You won't want to cancel the plan and lose the remaining "trade-in" payments.

What I have since discovered is that I will save more money if I switch to another cheaper carrier and forfeit the remaining "trade-in" payments. Unfortunately I'm still lost about $800, what Apple would've given me for my old phone.