Upgrade programme
I am in the upgrade programme and can upgrade anytime now! Can I just hand my handset in and clear my balance without upgrading? Or do I have to upgrade to a new handset?
Question marked as
Here are the (U.S.) iPhone Upgrade Program Terms & Conditions.
iPhone Upgrade Program Terms and Conditions
You are not required to upgrade. You may terminate participation in the program when you like. Of course, if you owe money, you will have to settle at termination time. I believe item (7) above most closely addresses this - I am not a lawyer, and do not speak for Apple.