Speaking professionally with depth and power begins with proper breathing.

Although you have been breathing since you were born, you have probably not paid much attention to it. You need to be aware of the two types of breathing - diaphragmatic and costal.
Diaphragmatic breathing uses the full lung capacity while costal (or high chest) breathing uses only the upper half or third of the lung capacity.
Diaphragmatic breathing is the foundation of speech, the support that provides the power behind the voice. By using the full lung capacity, your body provides the energy that gives your voice its depth and authority and enables you to project with ease. By limiting the intake of air it deprives the voice of support and pushes the voice into the throat. The result is a higher pitch, vocal strain, and a voice that lacks depth and the ability to project.

Professionals can learn to master their breathing and vocal techniques, as well as learn valuable skills with Building the Power of Your Voice: How to Improve Your Voice to Command Attention & Move People to Action
http://101publicrelations.com/voicepower.html?utm_source=prideas&utm_content=voice_power