A great use for them
After some playing with them when I worked for Three, I settled on the music from 2001 (sorry can't remember it's name. Goes beeeeeeeep, beeeep, badam, dom, dom, dom...)
Anyway, the deal with these is that the phone rings once normally, then switches to the music. So people would hear "ring" then "beeeeep" assume the call had dropped/gone wrong and call someone else.
Lo and behold my quotient of annoying calls from people who didn't know me but wanted to ask pointless questions dropped hugely. I'd still get the first ring while the phone was in my pocket, but if I wasn't too quick on the draw, they went away.
I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them, I love them.
(Sorry, couldn't resist.)
It's the next best thing to the people who are asking for a "f%£$ off" "ring tone" (as I think 3 were calling them then.)