I just received an audio postcard from Debbie Weil of WordBiz, and it fascinated me, so I took a look at the technology behind it. It comes from AudioGenerator, a service which converts phone-in audio into the ubiquitous Flash format.
Using Flash for audio provides for a markedly smoother user experience than any of the other audio formats. Compare the embedded audio clips (with no extra windows popping up at you) at the Audio Generator site with those (for example) at this Amazon page.
I’m still considering this, but you just might soon find my sales pages (such as that for “Surfnetkids Printables Club“) sprinkled with audio clips.