I upgraded early on my IUP plan (started May 2016, was tempted by the 8+, ordered it yesterday). I was told my old IUP was "frozen" and my new IUP starts when the iPhone arrives. When I send back the old phone, as long as I do it within 15 days, the old plan is cancelled.
Already got an email from Citizens saying loan approved for new phone.
I ASSUMED since I didn't pay for Apple Upgrade in a lump sum to start, that it was part of the monthly payment so I don't expect to get anything back when my old IUP plan is cancelled when I return my 6s+.
But I'm hardly knowledgeable about this as this is my first upgrade on the IUP plan.