The Apple blog published a nice article explaining how to create free ringtones using only the Apple iTunes software. The only restriction of that method is that the song needs to reside on the hard drive of the user so that a ringtone can be created from it.
The method is pretty straightforward but requires a [...]
Create Free Ringtones In iTunes
Get Free iPhone Ringtones from iTunes
This is probably not the best hack in life but it is still valid and working. You could use the ringtones for other mobile phones as well if you convert the m4p extension to a format that your mobile supports. The principle of grabbing song samples and use them as your iPhone ringtones is pretty simple.
