An application like that would not be allowed because it modifies the iPhone's OS. I don't know how Emoji got in, but they wont allow an app like lockdown. I've used lockdown, and its good, but if you put it on Messages and Safari, its put you into safe mode at time. If you get a text and click reply it puts you into safe mode, if you click on a homescreen bookmark it throws you into safe mode. A feature like this would have to be provided by Apple.