Good point, @chris.upjohn for some reason I didn't even notice the div
Looking at the styling you've got on that div though might be the key to what you're seeing. You've got your right/left margin set to auto; could it be iPhone's auto margin setting that's the root to your problem?
Also, not all mail clients render margin. Here's a great link @ronpat shared with me recently, make sure you're covered for the email browsers your readers use: http://www.campaignmonitor.com/css/