Link to this javascript in the head of the iFrame content document (the child document).

if (window.parent.screen.height >= 700) { document.write(''); } else { document.write(''); }

Of course this could be used for redoing the styles of the iFrame contents based on any other property of the parent document as well. For example you could say

Parent.document.body.some.property= 'a value"

window.parent.screen.height