If the iphone is your only camera, this could be very handy. Still, it diminishes the pocketability of the phone and I know I wouldn't carry it everywhere like my phone. I still want a GR with a 50 equiv. lens.Here's a phone grip product that showed up on dpreview today. It is actually shipping, and costs $40.00. It has a bluetooth remote and a stylus (?), but no knobs.
iPhone Stylus | Adonit Wireless Photogrip