After having the default sound effects for the first few weeks I finally made my own Blackberry ringtone and I'm using the intro to Shanice's "I Love Your Smile" for the sound effect ... it's the funniest thing being in a serious moment and then all of a sudden, "Do-do-do-do-DOO-do, do-do-do-do-DOO-do, do-do-do-do-DOO-do!"
You should see the looks I get in public when that happens ... but occassionally people know the theme and smile :D