Like the desktop one, except this time it's about your phones. Many phones these days have a screenshot function: try doing that someday! If that's not quite possible, posting just the wallpaper works, too.

My Samsung Galaxy S has a really boring home screen right now.

(Also note the ew-worthy dithering on the screenshot which is not apparent on the actual beautiful AMOLED screen)

Designing your pixel art based on 640x960 will do wonders.

It's a 2:3 ratio, so if you want it to look just right, without interpolation, you should try to make your art from something that's can cleanly divide 640x960, like 320x480, 160x240, 80x120, 40x60, 20x30, 10x15, 4x6 and so on. Then upscale it to 640x960 using nearest neighbour/no interpolation (latter term is technically inaccurate).