I can't believe the amount of people fooled by the AT&T Next plan...
Let's do the math: AT&T says that the Samsung Galaxy S4 will have a monthly installment fee of $32, on top of your existing AT&T service fees,
which already include a device subsidy. The exact amount of that subsidy is unknown, but most industry estimates have put it at something like
$20 per month. That's how you can get a GS4 for $199 with a new two-year contract, even though it costs $620 at retail: after two years, AT&T will have collected $680 in total device payments from you, and you get to keep the phone.
But the balance tips entirely towards AT&T with Next. Assuming that same $20 subsidy, after 12 months of Next you will have paid AT&T $384 in Next monthly installments and $240 in device subsidies, for a grand total of $620. Again, that's exactly the full retail cost of an unlocked Galaxy S4 —
but you don't get to keep that phone, even though you just paid full price for it. You have to trade it in to get a new phone — effectively giving AT&T a free GS4 to refurbish and resell to its next unwitting customer.
Now, you do get to keep your Next phone if you pay 20 monthly installments,
which will cost you a whopping $1,040 if you assume a $20 subsidy: $640 in Next payments, plus $400 in subsidies built into your AT&T plan. That's $420 in pure profit for AT&T, which just made you pay full price for a phone while charging you inflated service prices that include a subsidy specifically designed to lower the upfront cost of that phone.
source:
http://www.theverge.com/2013/7/16/4528404/att-next-phone-upgrade-plans-a-huge-ripoff