How would you like your phone to ring? A song? an Mp3 file? or other audio formats? Well, they are all possible on your Android device. to set a song as a ringtone on Galaxy S3 (or other Galaxy devices), do as follows:
1. Open Music Player (The default player on your device)
2. Browse for your favorite song and start playing it
3. Tap Menu Button and then select "Set as"
4. Now you have 3 options, which is to set the selected music file as Phone Ringtone, Callers Ringtone, or Alarm Tone