Most recent PCs have Real Audio bundled with windows. That means a large and growing number of your customers can click on your audio link, download your Real Audio file, and listen to it within a matter of seconds. Speak with energy when you record audio tracks. Because people can't see your face, your voice has to pack extra punch. Don't feel like you have to talk like an announcer.
Customers respond better to a voice that sounds like a regular person.
Several companies have created easy systems for producing and hosting your audio for free. The site rotates my talks, making them available non-stop 24 hours a day at no charge. I call it the Dr. Nunley Radio Network and link to it from my site. The Tenor MultiPath VoIP Gateway.