Requires iLife 08
1. Import a song into Garageband. * This can be a song from your iTunes library, CD, or something you composed in garageband.
2. Use the audio region editor to set your starting and ending point. * A ringtone can be a maximum of 40 seconds. If you don’t know how to use the arrange feature check out this tutorial http://www.apple.com/ilife/garageband/#arrangements
3. When you have your ringtone the way you like it go to the top menu and select “Share/Send Ringtone to iTunes” The new Ringtone will now show up in your Ringtones Library inside iTunes. Just connect your iphone and drag it to your phone.