I Bought a used one. The previous owner's email is still showing as NAI on the phone and his phone number is showed as soon as I connected to my itunes. So I went to a local Apple store and asked to replaced a UICC card by thinking this may solve the problem But no luck. I contact seller for a return since the phone seems to be tied up with his account still, but he refused because by his saying the UICC card replacement "damaged" this iphone and now it's useless. I am getting LTE signal but text messages about contacting Sprint request and the phone seems completely functioning. Can Sprint Care explains if the phone is still tied to his account and if it's still usable?