watch the kings speech movie or the video "musharaf finds his voice " on youtube. the latter is remarkable. starts speaking well when listening yo music. Stuttering when singing is rarely a problem. I think because 1. we know the words so don't have to think about what to say 2. We take a deep breath using the costal diaphragm when singing 3. and have to sing at the "top" of the breath to get the timing with the beat correct. also we are generally more relaxed when singing.