Personally, I don't like cell phone ring tones. I agree with the comedian who pointed out that ring tones, like pictures of your pets, may be cute to you but they're annoying to everyone else.
Nevertheless, I just heard a work that I wouldn't mind having as a ring tone. Composer and pianist Vincent Lo has taken the standard Nokia ring, and used it as the motif for a short fugue.
As you can hear (and see, if you read music), Lo's counterpoint is very inventive, yet logical. I think it works well as a piece of music.
You may here me air it on "Gamut" some fine Wednesday morning. But probably not on my person. Great as Lo's composition is, I'll most likely be keeping my phone in vibrate mode -- it's easier to ignore that way.