Importing Ringtones to iTunes

After you convert the song/sound to the AAC version (m4a), make sure to delete the AAC version of the song/sound in iTunes (while keeping the file). Then, after you rename the file to the Ringtone (m4r) version, you can import that file back into iTunes. Otherwise it won't show up in the "Tones" section and be 'syncable' to your device.