There are many ways to get free ring tones on your iPhone.  Mobile 17 offers a user friendly and free solution to filling your ring tone needs!  Just sign up for an account, and upload your sound clip (must be in mp3 format.)

There are two options regarding the speed in which your “order” will be processed.  If you choose the free option it can take a few hours, but with a small monetary donation you can have your new ring tone within minutes.  With either method you will receive an email with your new ring tone attached.  Opening the attachment dumps your new ring tone into iTunes and your are ready to synchronize. I have tried this service with three different brands of phone now and it works great!