Of course, it goes without saying (ha ha ha), that speaking too loudly will irritate your listener!
A smooth, easy cadence when speaking will endear your listener to you and what you have to say. Make a choice to use a natural, friendly and pleasant voice.
Be aware of your voice and how it sounds. When you have a smile in your heart, it reflects in the tone of your voice. Which brings me to CELL-PHONES!

Cell phones are a technological privilege that most of us, of course, find useful in our day-to-day lives. At the same time, however, many people agree that cell-phones have also created an unwanted intrusion in our lives.
According to a recent article in the Washington Post, a transit police officer arrested a woman who was disturbing the peace with loud cell-phone talk. She has been charged with disorderly conduct and resisting arrest.
Sakinah Aaron had, in George Saoutis’s view, been talking just a bit too loudly into her mobile as she walked into a Metro station in Washington DC. He told the pregnant 23-year-old to lower her voice - and was promptly informed that he had no right to tell her how to speak. There followed a verbal exchange and some pushing and shoving before Aaron found herself stewing for three hours in a cell.
Eventually, she was released but the Transit Police say the officer was protecting the peace by removing a woman who had overstepped the boundaries of civil behavior because she was loudly cursing into her phone.
While some free speech advocates say it's the Transit Police who overstepped boundaries, others believe that when it gets to the point where people are not using proper speech etiquette, the proprietor of a closed space has the right to enforce the etiquette.

Here are a few guidelines to follow in cell-phone etiquette, which we can apply when speaking face to face with a person, as well:

Speak softly and gently so you may not disturb others
Keep your distance from other people
Keep you conversation private
Keep a civil and pleasant tone
Turn off your cell phone or put it on vibrate or in silent mode where it would be rude if a phone rang. (such as at the movie, or during church - for heaven's sake!)