PocketMac RingtoneStudio for iPhone lets you turn almost any media file on your Mac into a ringtone, according to the developer. It works with sound files, unprotected iTunes tracks, and Mac-friendly movie formats.
If the track is 30 seconds or less, the software converts it automatically into the right ringtone format. If the track is longer than 30 seconds, a preview window appears so you can select the exact 30 second clip you’d like. Once you’re finished, the utility places your completed rington into iTunes’ Ringtones folder, which is then transferred to the iPhone the next time you sync your iPhone.
System requirements call for Mac OS X 10.4 or later.