Disregarding the fact that chalkdust is torture for your iPhone (dust+electronics=not good), anything you write on the conceptual design iBlackboard chalkdboard iPhone case will be useless anyway. Follow my vision here; as soon as you put your phone in your pocket, the soft material of your pocket will act just like an eraser. Bye bye message. Not to educate somebody’s fright here but yes drawing on your iPhone case would be cool but mixed in with the signal you’re sending is the torture of chalkdust inside your phone. If only I could unlearn the facts that I’ve learned. Make this dry erase and you’d be on to something though.
Just an idea, but you can DIY this exactly the same way with a cheap iPhone case and a little Chalkboard Paint.