The Verge was granted access to Microsoft's model shop where super-top secret prototypes are created. While the 3D printer used to create these prototypes is really cool, towards the end of the video (around the 3.36 mark). It may not be an actual working Windows Phone but the clear case is definitely an attention getter.
The clear Windows Phone was created to highlight the screen and likely never got any further on the drawing board. Still, how well do you think a clear cased working Windows Phone would go over?