Here are the instructions for Samsung a930.. I'm not sure if it'll work for other models... try it out...

-Go to the MENU
-Go to Settings and tools
-Press #
-Enter all 0's

-at this menu, press 0 again
-enter the following passcode 8886573982
-scroll down and select MP3

it will now look for mp3 files on your card... you need to reformat your card if you've already used it and make sure you put your music in "my mp3" folder...

Try it out!