- Start iTunes and find the song you want to convert. (It must be an MP3.)
- Right-click the song and choose Get Info.
- Click the Options tab.
- Check the Start Time and Stop Time boxes, then enter times for each (no more than 30 seconds apart, the maximum length for a ringtone). I used 0:00 and 0:30, respectively, as "Spit It Out" has a perfect ascending lead-in.
- Click OK, then right-click the song again and choose Create AAC Version. You should immediately see a new 30-second version of the song.
- Drag that version out of iTunes and into the folder of your choice.
- Delete the 30-second version from iTunes and undo the Start Time/Stop Time changes to the original.
- Open the folder containing the 30-second AAC file you dragged out of iTunes, then change the file extension from .m4a to .m4r. Double-click it and it immediately gets added to iTunes' ringtone library.
- Finally, sync your iPhone. When it's done, you can head into the settings and select your new ringtone.
In iTunes, go back to your library and go into the "Ringtones" (under Library) - you should see the ringtone you've just created - now click on the ringtone and drag it right down to your "iPhone" (under devices) - NOW your iPhone should sync automatically, if it doesn't, start a manual sync. You should now be able to go into the "Ringtones" under iPhone and actually see your ringtone - in short once you've created your ringtone in the normal way you then have to drag it from the "Library" section into your "iPhone" section in iTunes!!!.