I dont know what the "FAN" discount is ( i'm sure I could find out if i took a sec) bit you should be able to contact att about it. I had a media basic bundle with my old phone and i just confacted their support when i activated my iphone just to make sure it was removed in favor of the iphone data plan.
Hope that helped.
Simply an FYI, but I have the MediaMax bundle with my iPhone and still receive the FAN discount through my work. Maybe you should call AT&T, and without mentioning you have an iPhone, figure it why you're unable to apply the FAN to the Media Max plan.
May want to switch SIM cards (to a different phone) for the call if you call AT&T, the first question they asked me (before I said I had an issue) was if I had an iPhone. Scary stuff. I said no, got a confused salesperson, and got my question taken care of...