Phonebloks: A modular phone you update a piece at a time
news.cnet.com
news.cnet.com
As a related aside, in contrast to iDevices, the Galaxy S3 is the closest thing to a fully user-servicable phone I've found on the market. (hopefully the S4 is the same). Once you've unglued the glass one time, you can easily replace internals like both cameras, all buttons, glass, speaker, digitizer, etc, as well as the back cover and battery as designed. The parts are dirt cheap on eBay. I don't even use a case - there's no need since you're not hauling around a $700 glass-like block that you will inevitably break.
Discussion on reddit: http://www.reddit.com/r/electronics/comments/1m4m0f/this_is_...
This is not a good idea.