You have to pay off the rest of your lease in full AND THEN some. For example, I called earlier this month and was told that I still owed about $168 on my iPhone 7+ 128 GB that I got during pre-orders last year. If I wanted to pay it off and end the lease, I would pay the $168. If I wanted to pay it off AND be able to keep the phone, I owe $360. Essentially, we're paying installment payments on a fraction of the phone, not the whole cost of the phone.. hence why it goes from $168 > $360.
I also totally agree with this. I've been going back and forth with what I want to do. I'm almost 99% sure that ordering with TMO again this year is going to be a hot mess, just as it was last year. I remember being at a bar last year during pre-orders and having to stand on hold for an hour just to have the rep cancel my order on accident. I didn't get my phone until almost a month and a half later.
Right now I'm looking at stuffing the cost of the X on my American Express. Apparently they have this new "Plan-It" feature where you can make the phone payment in installments of 3, 6, or 9 months at a small % interest (I think mine was like .74% a month). Now, the only downfall of this is that I obviously will be buying the rest of my 7+ and selling it off, therefore taking myself off of JoD. If, which I don't doubt, Apple releases X version 2 in the larger size, then I'm going to want that which makes JoD useful as I can just turn in X (2017) and be on my way with the newest version.
It's just sad how TMO is such a mess when it comes to Apple releases, honestly. It's already going to be the week of pre-orders and we still have no information as far as pricing, ridiculous on TMO's part.