Other
Great voice.com
Berkley Productions at GreatVoice.com helps train voice professionals. From this page you can link to free subscription forms to two ezines. Under each form are links to sample articles, several of which pertain to tone of voice.
University of Pennsylvania
U Penn Library: Dreiser's Critical Reputation
A scholarly paper on Theodore Dreiser's "Sister Carrie" and the problem of using words to communicate as opposed to tone and other non-verbal means.
Other
Baby Center, Inc.: Babies and Tone of Voice
Baby Center, Inc. offers a quick question and answer about whether babies can understand tone of voice.