Create custom ringtones for iPhone 3G, 3Gs, iPhone 4 Using iTunes

1. Import the ringtone into iTunes

2. In iTunes go into Preferences > Advanced > Importing

Set to Import using: AAC encoder 128Kbps

or

3. Right click on the file you want as a ringtone and select: Convert selection to AAC

Your file will now be converted to an AAC file. (appears in iTunes under your original file) - call it a different name, so as not to confuse, ie: instead of Song.xxx, call it Song1.xxx

4. Right click on the new file, click on show in finder (or open folder on Windows Explorer)

5. You will now see your AAC file, all you have to do now is change the file extension from .m4a to .m4r

6. Drag the file out of the folder to the desktop, then drop it back into itunes. (Hover over your 'Ringtones' in the left menu list of iTunes, or it will just go into your main library)!

7. Sync with your iPhone.

8. Done.