Shaun Dailey might be described as a talk-radio veteran, but when he heard John Kerry on the other end of his show’s call-in line a few weeks ago, any listener could tell that he was slightly taken aback. “Oh...Senator Kerry, welcome to the program!...”

Their conversation took up a little more than eight minutes of Dailey’s hour-long show, and focused on Kerry’s support for Barack Obama’s presidential bid in advance of the Nevada caucuses. It would have felt like any talk-radio broadcast—if not for the fact that it wasn’t technically radio.

Dailey’s program airs on BlogTalkRadio.com, an enterprise that, in 18 months, has become the dominant player in the latest media trend, one that allows anyone with a Web connection to host a talk show on any topic at any time of day. It is the newest form of new media; the audio version of the internet blog.

“Everybody in our world—when I’m talking about our world I’m talking about over-the-air broadcasting and our media universe—is obviously watching this phenomenon closely and adapting as we go along,” says Dennis Wharton, spokesman for the National Association of Broadcasters.

Aspiring broadcasters log on and select the length, time slot, genre, and topic of their show. BlogTalk provides the internet broadcast capability and a telephone system that allows hosts to take live callers, all for free.

It sounds like the kind of service that would draw U.F.O. watchers and religious prophesiers—and it does. But internet talk radio is also rapidly getting attention from prominent hosts, guests, and broadcasting companies—especially in the wake of the blog phenomenon, which mainstream media outlets were slow to accept.

Two months ago, Arianna Huffington hosted a one-time BlogTalk program on which she interviewed Brad Pitt about the continuing struggle to repair New Orleans. Presidential contenders, including Mike Huckabee, Mitt Romney, and Rudy Giuliani, have been guests on news and political programs such as Dailey’s BlogTalkRadio Today and Ed Morrissey’s Heading Right Radio with Ed Morrissey. Not too long ago, Yoko Ono appeared on a BlogTalk show to plug—well, nothing in particular.

With its 40,000-plus shows, BlogTalk can bring in more than two million listeners each month, according to the company. In December, the site enjoyed about 80,000 listeners a day. That makes it a gnat compared to, say, National Public Radio, whose listenership over the last year has remained steady at 26 million. But BlogTalk is one of a half-dozen startups hoping to dominate the online talk space, and it has been growing fast.

“I think that [BlogTalk] represents something that’s far greater than itself,” says Michael Harrison, publisher of Talkers magazine, a leading talk-radio-industry trade publication. “There’s a whole bunch of new Web-based entities that I predict will be the media stations of the future.”

Among BlogTalk’s competitors are Skypecast.com, which is an offshoot of the internet telephone service Skype; Waxxi.us, which was launched in May 2006 and advertises its service as “interactive podcasts”; and TalkShoe.com. The competition isn’t quite direct. According to Waxxi founder and C.E.O. Tracy Sheridan, the company’s broadcasts usually include about 100 or 200 “listeners,” all of whom can participate in the conversation, which makes Waxxi more like an online conference call than an online radio show. The idea behind Skypecast is similar. That company describes itself in its promotional materials as “a live voice discussion about any specific topic hosted by one person that can include up to 100 other people participating from anywhere in the world.”