clipped from: www.iphoneringtonemaker.us Free download iPhone Ringtone Converter and install it.
Step1: Click "Browse" button to add files you want to set as iphone ringtone.
Step2: If you want a music clip by dragging the two slider bars or change the number to reset start time and end time.
Note: Click "Pre-listen" button to pre-listen the music clip.
Step3: Change destination folder by clicking "Browse" button.
Step4: Now click 
to start the conversion from MP4 to M4R Ringtone for iPhone. All conversion will be finished in a few minutes
Tips:
1. You can edit the added iPhone ringtone by click "Edit Ringtone". It's easy to rename the ringtone or remove it from your iPhone directly. 
2. If you have connected iPhone with PC, check the "Export to iPhone", WAV to M4R Converter can load converted M4R ringtone to iPhone directly.