Most "demo" or "dummy" phones that are sold online at places like eBay can not be used for cell phone replacement parts for their real counterparts.
I had a tear in the rubber alpha-numeric keypad of my almost new Centro and decided to take the risk and try using a demo for parts. I had read on a forum online that the case was identical to the original phone. That is definitely not true. The demo would suffice for the rubber keypad cover, the stylus (although it feels lighter and is a different hue than the one that came with my functioning phone), and perhaps the buttons used for navigation and the on and off buttons on the front of the phone.
Just slip a thin screwdriver under the rubber keypad cover to pull it off and replace the damaged one. The case, screen and battery cover can definitely not be used to replace any parts on the phone.