I don't use that title lightly. Over the weekend, I called someone who uses "ring back tones." Instead of hearing a ring, I heard a song. Granted, it's a clever idea, but to replace feedback that has been conditioned into callers for years is insane. Instead of thinking someone will pick up, I wondered if I got the number right, and not even by my own choice, a la ring tones.
Never inflict "nifty" on people at the expense of usability.