Trade-in value

No. Your trade in value is the remaining payments you don't have to make. Yes, depending on the phone, that may not be as much as your phone is actually worth. That is especially true for iPhones. In most cases you would be better off paying off the phone completely, get it unlocked, then sell yourself. 

The trade in value that AT&T is offering you is 6 payments.  

You could probably sell it for more to Gazelle and even more on eBay (or best to someone you know without paying a comission).

They're going to offer you less that you can get (they going to sell it to someone else), just like Gazelle is going to offer you less than you could sell it for on eBay.

Don't trade in an iPhone yet    Check the value against the same model and condition on eBay. 

If the phone is selling on eBay for much more than the amount ATT is forgiving, sell the phone.

Most people are selling their phones after one year and getting 75% of the original price, which is more than they owe.

My experience on the resale is when you pay an extra $100 (or $200) for more storage, the buy back places really don't help you out.  Many times I'd only get offered $10-$30 more for quadruple the memory (which was $200 more in the first place) than the standard iPhone, I'd do way better on eBay in those cases.

It's been my experience that E Bay is better than "trade in". My question related to the remaining payments. ( 24 month upgrade vs 30 payments ) Based on all I've learned AT&T Next & similar plans are not a good deal for the consumer. 

@TheNomad

I agree selling on eBay is better than trading in an iPhone.  For non iPhones it's often better to trade in as they don't hold their value as well.

I disagree that Next is not a good deal and the math proves it is at worst a break even, at best it is $200 cheaper than contracts were.

The best option is to buy outside ATT, but non carrier phones often cannot take advantage of all the services that ATT phones are programmed to use.  (iPhones do not have the same limitations as other phones)

Here is an example to compare Next with contract purchase of a $650 iPhone. 

If you buy at full price ....
$650 plus sales tax

If you use Next...
$650 in up to 30 installment payments. Sales tax is due up front and a $20 upgrade fee is charged.

~~~~~~No longer offered.....

On the no longer offered 2 year contract on the Mobile Share Value plan, I would lose my $25 line discount for 2 years, total $600. ATT charged $200 down payment price and $45 upgrade fee. Total without counting the increased taxes and fees over 2 years is $845.
Read that again, over 2 years family plans were paying $845 for a $650 phone.

For customer on smaller data plans and lower discount, it works out as a break even
$200 down, and the $45 upgrade fee, $360 loss of discount over 2 years, and the higher taxes and fees, total about $650. If you live in Florida or California where taxes and fees are really high, you will pay much more.

For customers who keep phones longer than 2 years, pass phones down to kids, this is a real bargain. Prior to the Mobile share value plan all line fees were $40 no matter what.

For my iPhone I'm tempted to pay the premium and do the yearly upgrade option.  I always upgrade every two years anyways, partially because of resale value and I want the new one (and I was paying for it with no choice the old way).

Instead of selling my iPhone for $200-$250) every two years just trade it in every year for the new one.

Either that or try to get a new person on my plan every two years and split the BOGO offer with them, 1/2 price iPhone and another person to share the cost of the phone with.

I'm way off topic now aren't I...?

Not at all...