Did you know that you can play your MP3's in the background while running other apps? Well, you can!
Launch the Audio Player app, click the Menu button, and select Options > Preferences
Next, check the "Enable Background Play" option and ckick "OK"
When you launch another app, any playlist currently playing will continue to play! Just re-launch the Audio Player app to adjust the volume, stop the playing, or select another song.
Just be aware that MP3 playing will cause quicker battery drain as well as slowdown in some apps (like games.)