I ordered a book called "freeing the naturol voice" by Kristin Linklater from amazon.com or barnes and noble I forget which. It deals with training the speaking voice for stage and screen, and is a very popular text in acting schools. Some people would consider it the bible of voice traing. It aims to provide a series of excercises to free, develop and strengthen the voice. It also address psychological issues that diminish the efficiency of the natural voice to the point of distorted communication. Do a search on it.