Pandora's growth doubled after it launched on the iPhone, announced Tim Westergren, the company's founder and chief strategy officer, Tuesday.

"Overnight, it completely transformed our business," Westergren said at the Web 2.0 Summit in San Francisco.

Pandora's founder explained that the service, which has been around for 11 years, transformed from a simple desktop computer radio to a real radio because of the explosion of mobile. Users started taking their iPhones and plugging them into their cars and living rooms. Seventy percent of Pandora use now occurs on mobile devices.

Westergren said Pandora is "radio-at-large" By that, he means that, unlike traditional radio stations, Pandora can serve a wider variety of music. The company has more than 900,000 songs in its library, and 95% of those songs were spun in July.

"It's really addressing the long tail," Westergren noted. "Most of that music doesn't get played on radio."

Westergren isn't worried about the rise of Spotify, Rdio and other music streaming services. He claimed that 80% of the time spent listening to music is spent on radio, while only 20% is spent on stuff that users own, including on-demand streaming services like Spotify. Westergren also argued that radio and on-demand music aren't competitive because most people use them in tandem.

As for what's next? "Obviously cars are a big arena for us," Pandora's founder said. "Half of music listening happens in the car." He explained that it would take a long time to penetrate the car market, since people don't buy new cars every year like they do smartphones.