Context: We moved a number from one plan to another, but the device remained on the same plan. The device remained on the same plan that it was originated on, and received a new number immediately. Again, no device was bought out as the device remained on the plan.
Problem: We had a $500 charge show up on our monthly bill that was labeled as "Device payment buyout charge". We strongly believe this to be an error, as nothing seems to be mentioned anywhere that switching numbers for a device would trigger a buyout charge. It mentions "disconnected lines" ,but we never changed our plan (meaning we kept the same number of lines because the device received a new number on the same plan)