1. Music activates the right side of the brain and language utilizes the left. Therefore when you sing, you are no longer relying upon your left brain and will less likely stutter.
2. When a person sings they use "easy onset" which is also sometimes called "easy voice", "smooth speech", or "relaxed speech." This is actually a strategy used by speech therapists. When we sign, we naturally use a smoother and easier voice than speaking.
3. In singing, words a prolonged and therefore less likely to be stumbled upon.
4. Generally speaking, when a person who stutters speaks differently than the way he or she usually does, they will more likely be fluent. This can also be demonstrated if the person uses a stage voice, foreign accent, dialect, whispers, uses baby talk, speaks slower, or uses a higher or lower pitch than normal.
5. So do you want to see this demonstrated? Check out Lazaro Arbo's audition for American Idol to compare his speaking voice with his singing voice.