The "Audio Ads" program was launched a while ago to a limited set of beta testers, but according to Barry Schwartz of Search Engine Roundtable, it's beginning to show up in most AdWords accounts. Check out Barry's blog for a step by step screenshot gallery.
The service looks very easy to use, and if used right, it could be an invaluable tool to help increase brand awareness. You can find professional talent in your area through the service, or upload your own audio advertisements to be played. According to at least one poster in the Webmaster Word forums, if you set a low CPM rate for your ads, you best optimize it for sleeping Alaskans.
Just like with anything else, the less you spend the worse the ads are. When I lower the cpm I end up with a lot of ads in Alaska between 1am and 3am. but I’m ok with that for testing purposes.