As the subject says it's free until 5/31 for existing FIOS customers... If you dont have it, perhaps you can call them and refer to the promotion. and yes, YMMV. good luck in getting it enabled.
Enjoy premium programming until May 31, 2013.
Thank you for being a loyal FiOS® TV customer! As a token of our appreciation, we are now including HBO® in your FiOS® TV programming package until the end of May. There is no additional cost to you and no action is required.
Simply tune to channel 899 HD (400 SD) to start watching the best Hollywood movies and award-winning original programming. We will automatically remove it for you after May 31, 2013.
Please enjoy the best programming FiOS® has to offer and let us know by the end of May if you want to keep watching HBO®.