mother fucking deek here:

Once you make your Mp3 clip, you need to right click on the filename in Windows Explorer and Rename the extension from .mp3 to .3gp and save it. Then send it to your phone or put it on the TransFlash card and put that in your phone.

Now if you cannot see the filename extensions (i.e. all you see is my_song and not my_song.mp3, you need to go to View at the top of the Explorer Toolbar and select Options and uncheck Hide file extensions for known filetypes and then Okay. Now you should be able to see the .mp3 at the end of the filenames.

Credit: Howardforums