Stop me if you've heard this before

So I was thinking to myself last night, the reason a camera is so expensive is partially ( a big part) the lense and sensor, and also a big part the processor and logic behind the scenes that adds in all the cool little tricks modern digital cameras can do.

Now the iPhone has a good enough sensor and lense, and in the world of cameras super overkill in terms of ram processor and memory, now building on that, is there any reason we haven't seen a full fledged professional, or at least prosumer device where you slot your iPhone in and it basically becomes the screen and processor for a professional lense and sensor set?

With all the cool things you can do with the existing apps on the iPhone like multi exposure HDR photography and any kind of filtering effect you can imagine all the way up to photoshop on the iPad, it seems like having something like this would be a great way to build a really great camera at a low price by letting an iPhone app handle all the logic so you don't have to include several very expensive pieces in your digital camera's production.