Yeah, there's a lot of things we don't know since Gizmodo only had the phone, not the skills. But they did say it appeared to be ceramic, and a MR poster who works with ceramics for a living was 100% convinced it was zirconia just from examining the pictures, and we also have that patent application from 2006, so I'd say there's some pretty good evidence even though it's not entirely conclusive. And finally there's the design of the prototype itself which appears to be tailor made for heat dissipation through everything *but* the back. Of course, Apple may also have made the aluminum body just for the heck of using aluminum again, but still, the design supports, or at least doesn't contradict, the zirconia theory.