Here's how that will work:
First of all, you have to have been enrolled in the program at least six months and have made the equivalent of 12 payments (so if you haven't made 12 yet, you'll have to pay the difference to upgrade your phone).
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Assuming that condition is met — and you still have your phone to trade in — you can make the exchange at a nearby Apple Store. You'll need two forms of ID, plus a credit card and your Social Security number (they will run a new credit check). And you'll need to know your current wireless account password.
If your current phone is damaged, you can still trade it back, but will have to pay the AppleCare deductible for the type of damage it has.
It's also a good time to consider if you like your carrier, as the Apple Upgrade Program also allows you to change providers anytime you want. And there's a reason to think about this now.
Last year's iPhone worked on all four major carriers. This year, Apple has two models, so if you get the one for AT&T and T-Mobile, it won't work later on Sprint or Verizon.
Also, remember: You don't have to trade in your phone. Technically, you are buying the phone in 24 equal payments, so another option is to keep the phone you've got, and after two years you will own it outright. If you trade it in for a new iPhone, that two-year clock starts over.
Apple has more details on its site, as well as a way to check whether you are eligible. Still not totally clear is just how Apple will decide who gets priority for the new iPhone among those who are upgrading, those new to the program and those buying a phone outright.
Many carriers also have their own early upgrade programs for those who buy or lease a phone through them. Sprint, in particular, last year launched its iPhone Forever program, which gives people who lease an iPhone from Sprint the right to trade in for a new one every year.
If you are thinking about the new iPhone, whether or not you are part of an early upgrade program, there are some pretty interesting limited-time offers from the carriers.
T-Mobile is offering those who own an iPhone 6 or iPhone 6s the option to trade it in for a free iPhone 7, as is Sprint.
AT&T has its own free iPhone 7 offer, but it's got a lot more conditions. You have to be an AT&T television customer (or sign up for new service), transfer a line to AT&T and trade in your old smartphone.
Update: Apple says that eligible upgrade program customers will be able to reserve an iPhone 7 when preorders begin on Friday.
—By Ina Fried, Recode.net.
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