In February, San Diego-based Slacker broke away from catering just to core music fans and changing its service with mainstream consumers in mind, giving the service more visual elements, adding more personalized recommendations in order to appear friendlier to new users who may not know exactly what they want to listen to next.

“Listening time since launch has also gone up by 25% largely because of the more approachable interface and new programming,” Slacker chief executive Jim Cady said. “We had expected it to go up. We didn’t expect it to go up that much.”

The addition of new subscribers represent between 10% and 20% for Slacker, which has somewhere between 500,000 and 1 million paying users in the U.S. since its Feb. 13 launch. Slacker has more than 35 million registered users, but does not disclose how many of those users continue to actively use the service.

Slacker also reported that two-thirds of its listening hours now come from mobile devices, the next area of focus for the company as it continues to button down deeper deals to bundle its service with cell phone carriers such as AT&T, Verizon, T-Mobile and U.S. Cellular.

In the long term, however, Slacker is aggressively pushing into connected car info-tainment systems, working with Ford, GM, Chrysler Group, Acura, Honda, Scion, Subaru and Tesla.

“Mobile is important to us because it’s the gateway to the car,” Cady said. Slacker has also been steadily accumulating non-music content in order to compete with broadcast radio in the car, including comedy, national news and live sports coverage.

In the Tesla S, where drivers can tune into Slacker without having to tap into the data connection from a smartphone, the number of hours spent listening to the service are two to three times longer, with some listening more than 100 hours a month, Cady said. [Billboard.biz]