Not Sure
I use ATT Next, I am not sure why you would use anything else. You get the phone you want with only the taxes down then interest free for 20 or 26 months with the ability to pay it off at any time. I would much rather hand Apple $60 than $649. I still have the option to leave ATT at any time just would have to pay for the phone, there really isn't a down side to it that I can think of other than the phone is locked until it is paid for and you request an unlock.
I use ATT Next, I am not sure why you would use anything else. You get the phone you want with only the taxes down then interest free for 20 or 26 months with the ability to pay it off at any time. I would much rather hand Apple $60 than $649. I still have the option to leave ATT at any time just would have to pay for the phone, there really isn't a down side to it that I can think of other than the phone is locked until it is paid for and you request an unlock.