Source: cnet.com.au
This doesn't mean we should have to pay for them. After paying higher than average prices for iPhone contracts, are you really about to fork out more money for 15-second clips of your favourite songs? We don't think this is fair and to right this injustice we show you how to make your very own iPhone ringtones for free. All you'll need is an iPhone (of course),iTunes and a swag of MP3 files.
This will open a new dialogue box showing various details about the audio file. Select the Options tab.
This will return you to your music library.
iTunes will process this briefly and insert the new ringtone-sized file under the original file in your library.
A new dialogue box will open showing you the location of this file. Select the file and rename it, changing the file extension from ".m4a" to ".m4r". Windows will warn you that this change may make the file unstable, but continue anyway.
Back in iTunes, delete the ringtone file you've created from your library, then import the renamed ".m4r" file into your library. Connect your iPhone and sync your playlist. You may have to manually drag the .m4r file into the Ringtones section on your iPhone. With your iPhone synced this file is now ready to be used as a ringtone.