I received this offer in the mail for one of my Amex cards, and I called Amex for each of my cards (separately) and signed up all of my personal and business charge card accounts for this offer (although it seemed to have only been targeted to one of my business accts). The offer that I recevied expires 2/15/14, so I would encourage everyone to take advantage of this now. There's no guarantee that they'll sign you up, but it seems that if you tell them you recevied the offer in the mail, they shouldn't give you any trouble.
The number I called (for OPEN) is 800-492-3344. See attached letter for offer info.