Much as I like the Yoko Kanno reference, I actually keep a better-known piece of his as a potential ringtone: "Tank!", a jazz piece he made with a group called The Seatbelts. I actually use different ring and notification tones to tell me the nature of the incoming transmission. My generic ringtone is the theme from Beavis and Butt-head (which is actually a nice-sounding smooth-paced piece of instrumental rock), and my notification tone the doorbell from Star Trek: The Next Generation (quick and easy to catch). If I hear something else, I can determine its nature quickly (work, acquaintance, app, etc.).