Question: how to set custom mp3 ringtone in iphone?
Answer: Step One: Get iTunes. You almost never have to use iTunes with a modern iPhone, but adding your own custom ringtones still requires it. ... 
Step Two: Choose a Sound File. ... 
Step Three: Convert the MP3 to AAC. ... 
Step Four: Rename Your AAC File. ... 
Step Five: Add the Ringtone File to Your Phone. ... 
Step Six: Choose the Ringtone.