I'm not sure that's how the program works. You signed up to make 24 payments on your phone. After 12 you can upgrade and when you do, you'll get a fresh 24 months to make payments again. You didn't lose out on anything, just delaying when your new 24 month contract begins. It's really just a 2 year loan on an iPhone that you can trade out and start over with a new phone after 12 payments.
You do lose. Let me show you the math.
You sign up Sept last year for IUP. You pay one payment upfront, plus taxes, and then you make 11 payments over the course of the year and now it's Sept 2016. You've paid 50% of the purchase price of the 2015 iPhone and have met all of the terms of the deal which states that you can now surrender your old iPhone back to Apple and start a new 24 month contract on the 2016 iPhone.
If you don't get to purchase the phone until October, you now have made 13 payments and your 2 year contract for the 2016 iPhone begins in October. If you want to order a 2017 iPhone in September, you have only made 11 payments during that time period and you'll be required to make a 12th payment to satisfy the contract in order to place your order in September.
So you paid an extra month in 2016 and you'll have to make an extra payment in 2017 which means that Citizen's Bank collects two extra payments though you fully intended on upgrading every 12 months and Apple assured you that you could.
On top of that, your equity in the iPhone you have given back to Apple has increased with no corresponding recognition of that increased value. In other words, just to keep the math simple, if the iPhone costs $1000 and your monthly payments are $41.66. At the end of 12 months you have paid $500 and one assumes Apple can refurbish and sell the iPhone you turn in for > $500.
But if you ended up making two extra payments, you've paid $583.33 and Apple still gets the phone back which they can still sell for the same > $500 in essence making either Citizen's Bank or Apple an extra $83.33 with no real decrease in the value of the iPhone that you're turning in. Nobody knows if a refurbished iPhone is 1 month old or 13 months old so the value they receive remains constant while your equity is not the same.
Of course, most people who participated in the program understood that. Few would be dumb enough to hold the phone for 23 months and then turn it in under an upgrade when they could make one more payment and own it outright.
But what made the entire financing scheme attractive to users, and the way it was pitched to people, was make 12 payments and get a new iPhone. You essentially only paid $500 to use an iPhone for a year and in exchange you were willing to give up any amount greater than $500 you could have gotten selling your iPhone privately.