I've done a few of these before - white, aqua, cherry red, beige.... There's yellowed phones and then there's polane coated phones. I just used sand paper all the way - nothing else. 220 grit will cut into a polane coating pretty fast. If you're sanding out yellowing, you can even go to 100 grit for deep digging. 100 grit is *very* rough so you need to follow up with a diligent effort with the 220 grit. Delicate areas like cradle's and sharp edges, I wouldn't go less than the 220, though. Like Jorge, I didn't mess with the logo's/raised lettering... If your coating is the same as the plastic, usually this doesn't look too bad. If the polane coating is a different color, then you'll need some kind of chemical to remove it from the logo areas... I never looked into this...
Always wet sand. I usually sand at the kitchen sink with the water running. I cut a sheet of sandpaper into 1/16th's. Take an old yardstick and saw off about 2" - makes for a great sanding block for the 1/16 sandpaper squares (or rather rectangles). Of course, a lot of the sanding needs to be done without the sanding block. After the housing is completely sanded back to the original color, then you need to go over everything again with 600 grit or higher - this will prep it for buffing. I find 600 grit is the minimum I can use to buff out sanding marks with blue PBC (plastic buffing compound).
Practice helps - practice on something impossibly ugly or damaged. It's a lot of work.... labor of love, I suppose...
