SLR mount for the iPhone
Soon can buy an adapter that let you use your Nikon F-mount or Canon EF-mount lenses lenses on your iPhone! (It is not compatible with EF-S or FD lenses.) Details here.
This is a must have thing for those times you can't be bothered carrying a DSLR body, but still want to use your 70-200 mm f/2.8 telephoto zoom.
The device is really a special iPhone case with a ground glass and tube/mount. Your Canon or Nikon lens projects an image on the ground glass, and your iPhone takes a photo of this projected image.
You can attach all sort of SLR/DSLR lenses: zoom, telephoto, fisheye, wide angle, macro, etc., and since what you photograph is a projected image, depth of field will be the same as if you used the same lens on a SLR/DSLR. Imagine shallow depth of field and beautiful bokeh on an iPhone.
It comes with certain caveats: Your preview on the iPhone screen will be upside down (for USD 249, they should be able to bundle it with an app to flip it). The grain of the ground glass and any dirt on it will show up on the images. But the really bad news is that it does not have any electrical contacts, so you will not be able to control the aperture of a Canon EF-lens or a Nikon G-lens mounted on the adapter. Nikon non-G glass is what will work best.