Last year I have bought an apple care together with my iphone. Although my seller notified me that my apple care is pre-registered with my iphone, sometimes we really need to check whether it is applied. First thing is if you have a pre-registered apple care an email notification should be sent out indicating the end date of the premium support. If no email is sent out then user change check the apple support center (https://selfsolve.apple.com/GetWarranty.do)