ConvoCast is easy to explain to anyone who uses social networks and listens to the radio. It’s a sort of widget for a radio station Web site that lets a listener go to the site and talk with the host and other audience members by leaving audio comments over the phone or written comments.

In fact, it doesn’t look so different from Facebook’s interface, as you can see from the example posted with this story — a test the company made for a New England sports show.

Los Angeles-based ConvoCast’s idea is that there’s a large number of people who want to respond to radio shows and who can’t get through on the call-in phone lines.

The way ConvoCast works is that a radio station owner installs the company’s social network widget on its own site, on the homepage of a radio show. The widget and the site data are hosted on ConvoCast’s own servers. To counter abusive users, it also provides an administrative section, so a station can pull down offensive content.

The big difference between this application, and say, a podcast, is that the radio station has an established listener base and a sales team that already has connections with local advertisers. The ConvoCast widget includes space for banner advertising that a station’s sales team can sell to local advertisers, which may also prove valuable as a component of a larger radio advertising package.

A number of radio station owners and affiliated companies are interested in the offering, Convocast tells me. It is working with a number of undisclosed local radio partners to test the service out. It is also looking at offering Facebook applications in order to attract Facebook users to radio shows.