I got quite excited by these & bought a 'tremolo' one. Seems to be a few sellers out there with various designs (have seen distortion, metal and bluesdriver) to fit all phone types.
Not that easy to get (seems to be easier in the USA) or that cheap, but I'd bet I'm not the only one on here who'd get a kick out of these :) ::)
(http://ih0.redbubble.net/image.47147342.0168/mwo,x350,iphone_6s_snap.2u2.png)
http://www.redbubble.com/people/abinning/works/9530168-boss-tremolo-pedal-iphone-case?grid_pos=6&p=iphone-case (http://www.redbubble.com/people/abinning/works/9530168-boss-tremolo-pedal-iphone-case?grid_pos=6&p=iphone-case)