Apple offers on its website, a dedicated page: https://supportform.apple.com/200709/main?id=qp allowing early purchaser of the iPhone to claim their US$100 Apple Store Credit Bon. All you need is the AT&T telephone number associated with the iPhone and its serial number.
So, if you unlocked your iPhone and now expect to claim your Apple Store Credit coupon, you might never get it. If you know someone with an AT&T mobile phone, you can always try to enter is telephone number, with no guarantee that it will ever work.
[translation by Linathael]
