there are teachers who teach speach or speach arts, as I recall. This is what I quickly googled
http://www.mtroyal.ca/conservatory/speech.shtml
I remember when I was a kid, my parents took me weekly to some teacher who had me go through a curriculum of things like performing a monologue, acting/expressing in mime, or discussing a random topic. First it helps build confidence, two the teacher and ultimately an examiner (kind like for piano lessons, you get an exam at the end of each "grade" or "level") will judge you by the quality of your presentation, clarity of voice, enunciation and other criteria. I distinctly remember it was a curriculum from Trinity College
http://www.trinitycollege.co.uk/site/?id=139
Even a public speaking course or group such as Toastmasters would be a great place to practice speaking, and having others give you constructive feedback on how to improve. And if you don't, at least your will build some confidence. Sometimes it just takes a bit of confidence to move your voice from building in the throat to building from your chest and stomach so you project more clearly and with confidence.
hope that helps