I don't think there is anywhere to attach a charm to an iphone. If you're really desperate, accessory geeks sells an adhesive o ring that sticks onto a phone, so that you can add a charm. I don't have one though, so I can't speak to how strong the adhesive is.
Here is the adorable little devil that WON'T work with my iphone...It looks so great with my 04 PH black first, perfectly matching the pewter hardware. Maybe I Will keep as a key chain, albeit a very expensive one. It is just so exquisitely made, I can't stand to send it back.