Everytime someone pays for a ringtone a small part of me dies.
Ok, maybe that’s a little dramatic, but there’s no reason to pay for a ringtone. (As long as you’ve already own the song in question.)
Most phones will actually do this for you, but you usually have to read the manual to figure out how to do it. The other way to go is (of course) through the internet. There are dozens of sites that will convert music to a downloadable ringtone for you. Make sure you read the fine print and find out what their business model is. You don’t want to unknowingly sign up for some costly text-messaging scheme.
A good one I found out about through the New York Times is Cellware.
You can read more about in their tech blog here: http://bits.blogs.nytimes.com/2007/12/11/make-your-own-ringtones-even-with-copyrighted-songs/
So please, don’t pay twice as much as a few seconds of a song, just so you can use it on your phone.