Yep - did the trade-in last year going from 5s to 6.
I did mine last year in-store. I had to pay the remaining balance to be eligible to do the trade-in upgrade...it was like $120-something. Not horrible. I chose the longer payment plans to lower my bill. But this year I'm doing the 12 month plan so I can upgrade to the 7 next fall.
If you're not showing as eligible for Next upgrade yet, here's what you do:
-Go into your account online and choose the line you want to upgrade.
-You should see a some dollar amount that you need to pay in order to be eligible to upgrade WITH phone trade-in.
-Go through the process of the upgrade (this means picking a new phone to "upgrade" to, but you won't be upgrading today, don't worry - just making yourself eligible to use the Apple Store app/online store.)
-You'll come to a screen where you must pay that remaining balance in order to be eligible. It's a separate transaction and will ask for your credit card number.
-Pay that amount and then right after, cancel the rest of the "upgrade".
Wait a second, and check your eligibility through the Apple Store. Should be good to go!
