From apples site : Keeping the Outside of iPhone Clean To clean iPhone, unplug all cables
and turn off iPhone (press and hold the Sleep/Wake button, and then slide
the onscreen slider). Then use a soft, slightly damp, lint-free cloth. Avoid
getting moisture in openings. Dont use window cleaners, household cleaners,
aerosol sprays, solvents, alcohol, ammonia, or abrasives to clean iPhone. If
your iPhone has an oleophobic coating on the screen, simply wipe iPhones
screen with a soft, lint-free cloth to remove oil left by your hands and face.
Please note that the ability of this coating to repel oil will diminish over time
with normal usage, and that rubbing the screen with an abrasive material will
further diminish its effect and may scratch your screen.