To make the message bar "float" underneath the logo, you need to set the containing div css (#header-callout) to have position:relative;
and set the z-index to something negative (z-index: -1
should do). This creates a layering in the divs and puts the message bar below all other divs (unless you set something else to a lower z-index).
For displaying things differently on the iPhone screen size I would suggest using a media-query. If you don't know how to use those, I suggest browsing through this article to get a better idea of what I mean: http://css-tricks.com/css-media-queries/
In order to NOT display the message bar, you will have to put display:none
for the #header-callout in the css of the appropriate media-query.