This has been tested and proven over at Macrumors.
1. Create a ringtone as mp3 (less than 30 seconds long).
2. Import into iTunes.
3. Convert to ACC.
4. Rename extension to m4r.
5. Drag the file into the ringtones folder.
You can then sync your custom ringtone with your iPhone. It works like a charm.
Have fun guys and gals! I'm so glad that I can finally use CTU as my ringtone.
