Thanks in large part to mobile apps on both smartphones and tablets, Pandora announced today that it has passed a huge milestone as the site now claims 150 million registered users. That’s a lot of parties, wedding receptions, study sessions, and road trips that Pandora has provided a super personal soundtrack for.

Speaking today at the International CTIA Wireless 2012 conference, Pandora President and CEO Joe Kennedy said, “The continued growth of Pandora shows that personalized radio is fundamentally changing the way people listen to music.”

He also cited the importance of hand-held devices to Pandora’s success, saying, “Mobile connectivity has allowed us to deliver on our mission of providing people with music they love at a scale that presents unprecedented opportunities for both artists and advertising partners.”

Pandora owes much of its expansive growth to mobile accessibility, as more than 100 million of the site’s registered users have accessed the internet radio site via mobile device. More, over 70% of the hours of music listened to through Pandora happens by way of mobile devices. In fact, about one out of every three U.S. smartphone users now listens to Pandora on a monthly basis.

Just last month, Pandora provided a total of 1.06 billion listening hours, an increase of 87% for the same period last year. Given Pandora’s 51.9 million active users – up from 34.0 million the same time last year – Pandora users listened to nearly 20.5 hours of music on average in April. Share of total U.S. radio listening for Pandora last month was 5.95%, up from 5.79% in March and up more from 3.11% in April 2011.

Although Pandora missed analyst’s expectations for the fourth quarter and fiscal year in 2012, the company still posted a 99% growth for the year. As Pandora continues to establish itself in the mobile market, it’s likely the internet radio company’s growth and share of the listening market will continue throughout 2012.