1 Make sure that the phone number is the one that you used when you purchased the iPhone. 2  Then tap next. 3  Enter your billing zip code and the last four digits of your Social Security number. 4  Then tap Next. Make sure that the phone number is the one that you used when you purchased the iPhone. 2  Then tap next. 3  Enter your billing zip code and the last four digits of your Social Security number. 4  Then tap Next.