Pandora has finally hit scale, with a listening audience that has become attractive to advertisers, even in local markets where broadcast radio typically makes its money, said Pandora Founder Tim Westergren at Web 2.0 Summit in San Francisco Tuesday.

Part of this success, Westergren said, comes from the diversity of its music catalog, with several hundred million songs. And 95 percent of those were played in July, according to Westergren--a pretty stunning data point, and the company founder said most of those songs aren't ever played on broadcast radio.

The company's growth exploded in 2007 with the advent of the iPhone. "Overnight it transformed our business," Westergren said. "We almost doubled our growth rate" (measured in new registered users each day). "It changed Pandora from being desktop computer radio to being like real radio," because users took phones with them, plugged them into places like cars, and then Pandora become any time, anywhere radio. Westergren said 70 percent of Pandora's usage happens on mobile devices now.

Westergren considers Pandora a radio company, whereas services from Apple and Spotify are subscription music services. He said that most people use both, side by side, so Pandora does not compete with them. In fact, people may hear a song on Pandora and then go buy that song on iTunes.

Pandora is not interested in getting into television or video programming, Westergren said--or at least he hasn't seen a business model that excites him. However the company has seen success venturing into comedy radio programming, and he seemed a bit more enticed by parlaying that success into areas like news and sports talk.

The company abandoned its plan to charge users 99 cents (for unlimited content) after surpassing 40 hours of use in a month. That's because the advertising base grew in a way that continues to allow the company to subsidize listening, Westergren said.