Nokia has become the first major manufacturer to release 3D printable files so their customers can download, modify and 3D print components for their phone. Read about it on the Shapeways Blog.
This version is not printable due to the buttons, for a printable version please go to http://www.shapeways.com/model/877585/nokia-lumia820-shell-no-buttons.html
This is the Rear shell for Nokia Lumia 820 shell with all parts. It is available for 3D printing as is in Nylon, or you can download and modify the file with any cosmetic or functional feature you like.
Nokia has released this file under a Creative Commons License
You can read more about their file on the Nokia Developer site.
Please read Nokia's terms and conditions, and sharing protocol.