Question: how to set purchased song as ringtone on iphone?
Answer: Click on the song you want to use to make a ringtone in your iTunes Music Library. Click "Store," then "Create Ringtone." Adjust the slider to choose a song segment for the ringtone. You are limited to 30 seconds. Click "Preview" to listen to the ringtone. ...  Click "Buy" to purchase the ringtone.