Requires iOS 4.0 or higher
PowerPLAY makes your volume buttons useful.
It applies two simple tweaks to your iDevice:
1) Allow the volume to be changed on the lock screen.
2) Control your music with the volume buttons. Hold the volume down button to go to the previous track, and the volume up button to go the next track. Press both volume buttons to play/pause your music.
Volume buttons can still be held down to control volume while music is not being played
This is a stupid little app with a horrible name, but it's a tweak I can't live without so I figured I'd share :)
No new icons are added to your homescreen and there are no options to configure.