You remenber those transfers you used when you was a child, don't you? Here's a fun way to remember old times ;)
Ehm, DISCLAIMER: I used scooby doo tranfers because the WERE on a box of cereals I recently bought, but I'm SURE you'll find more fashionable ones XD
Remove the transparent plastic film.
Place the transfer on your phone.
Use a rubber to press the back. Move it as if you had to cancel the image.
Remove the plastic on the image.
Dip your fingertip into water and press it. Ta-da! Tattoed phone.