Results are in the preparation. Start be removing everything from the case that you don't want to paint, don't just mask or you'll have problems later. Next you'll want to sand the case down to bare steel starting with a medium grit paper. Work your way up to a fine or extra fine sandpaper to remove any scratch or swirl marks. Finally wipe it down with cheesecloth.
You'll want to use a good quality aerosol paint for metal, such as Rustoleum. Their black is very good but you'll want to match the luster of the phone to the paint before you start sanding away. Light, even coats, allowing dry time between, will prevent runs and sags. Do this over and over until it looks just right. If you want that "laquer look" sprinkle water on the case after it's fully cured a day or so and sand with wet/dry extra fine paper to knock down the smallest imperfections.
Wipe it down, reassemble and you're set!