For iPhone you have to buy the ringtones from the iTunes. However, with the given process, you can convert unprotected music files in to ringtones for free.
- Get the .mp3 or .wav file of which you want to make the ringtone.
- Open iTunes and drag the file into it.
- In iTunes, select the file.
- Open the Advanced Menu and click on the option of Convert Selection to AAC.
- Now select the AAC file. Go to File menu and click on Show in Finder.
- Select the file in the finder and go to File > Get Info
- Change the extension of file to .m4r from .m4a.
- A dialog box will appear to confirm the change. Press the button Use .m4r
- Now drag this new file in to the iTunes. You can find this ringtone in ~/Music/iTunes/iTunes Music/Ringtones
- Now connect the iPhone with the computer and tap the tab of ringtones.
- Select the newly created ringtone.
- Sync the iPhone with iTunes.
- Now the ringtone has been created. Set it as the ringtone in your iPhone.