You could also have the metal body powder coated! Local auto body collision shop should be able to handle it.
And no I haven't painted or sanded my phone. I only look at the screen so I really don't care what the back looks like. The screen looks awesome though! 4.3" SLCD glory! LOL!
I do paint plastic and metal. It's not hard. Proper preparation of the materials being painted is the most important part. It is painting 101; prep materials, good paint, tape off anywhere you don't want paint, hang part from thin wire or string, spray thin even coats, LET DRY BETWEEN COATS(dry to the touch is not DRY), lightly sand between coats if desired with ultrafine paper (clean part again before next coat if sanding), repeat.......
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