By off contract devices you mean full retail right? Because you are right there. However, in essence the Edge program is the same thing as paying full retail, just not all of it up front. Just like Next. But you could look at is with the credits as a benefit. But to each their own.
I'm not sure this is true...from the fine print I could find it goes something like this (and I'm just reading what I can read same as you...I don't work for any carrier, etc.)
They're both basically lease arrangements.
ATT Next has two options: "12 mo Next" and "18 mo Next". Each has a lease-contract that extends 8mos after the minimum-upgrade/plan date. Upon hitting the plan date (12 or 18mos), you
can (at your option) upgrade to a new ATT phone with a new lease-contract and if you return your "old phone" (I assume in working-order) - the one you're upgrading - they will waive the remaining lease payments on it. So you will pay more than a subsidized, $200 up-front, but less than full retail (but you don't keep the phone in that case).
What happens if you keep the phone until the end of the actual lease? I
think it's yours free-and-clear, and you've basically paid (roughly) full-retail for it.
Edge appears similar, except they are a 24mo lease with an option to get out after 50% paid (I didn't find it in ATT's lingo, but with VZ you can optionally pay more per month, or pre-pay months, or make a bigger "down payment"). So usually that implies that you can upgrade after 12mos -- and again, you have to return the phone to upgrade or buy it at full-freight -- except, if you're paying more, early, you can actually upgrade after 30 days or something crazy.
So I don't think either program is truly "like paying full retail" unless you ride the lease to its end -- which, like any reasonable lease contract, is your option.