Email HTML. Hide content on desktop but show it on mobile. This is tougher because Outlook 2007 (desktop) won't recognize CSS that you would use to normally hide something.

gistfile1.html

/* in your css.  (in this example, in the media queries specific part which is just for phone) */

@media only screen and (max-device-width:480px){
  *[class*="mobile-only"]{display:block !important;max-height:none !important}
}


<!-- this html section will only show on phones -->

<!--[if !mso]><!-- -->
	<div class="mobile-only" style="font-size: 0; max-height: 0; overflow: hidden; display: none">
        
            <div style="text-align:center;">
            <img src="logo.png">
            </div>
                                
        </div>
<!--<![endif]-->