Question about those participating in the Apple Upgrade Program. It is my understanding that after 12 months of payments you are eligible to trade it in for another phone. If you choose not to and you have made 24 months of payments, then you own that phone and your 'contract' is complete. What happens when you trade in for an upgrade at 18 months of payments? Does the extra 6 months go as a credit against the new phone? Are you refunded? Is that money now gone? Thanks.