Maybe some of you that don't have it are not the page administrator? I could not find the button on my smartphone, I have a feeling that those of you who didn't get the prompt probably will at some point, Maybe its being rolled out in us in stages...maybe the support teams get overwhelmed if everybody gets it at once, Also, try logging out and back in several times to see if it will trigger the prompt, Im not sure but I think when you make a post it it will incorporate the call to action button embedded in the post,,,or maybe that is wishful thinking If it doesn't,,,It may be a good idea to draw attention to it when you create a post, This blog claims you should change your cover photo on your page once a month to keep it fresh! Really!!Here is another article regarding the buttons, http://www.postplanner.com/facebook-call-to-action-button-for-pages/