Although iTunes remains a popular service for downloading and listening to music, it is quickly being replaced with free and subscription-based music services such as Pandora, Spotify, iHeartRadio, Songza and more.

Pandora has surpassed 200 million registered users in the U.S., which is up 100 million from July 2011. Despite the company’s move to limit mobile monthly usage to 40 hours last month, 140 million of its users are accessing the music service from a mobile device; one in three smartphone users tune into Pandora every month.

The company’s push in the vehicle market is helping its growth and mobile usage. It partnered with Pioneer in 2010 to provide Internet radio-enabled music systems for cars and since then has signed several deals with manufacturers like BMW, Ford, Mercedez-Benz and Toyota.

Approximately 67 million of Pandora’s users are monthly active listeners, which are the unique registered users that have used the service within the trailing 30 days from the end of each calendar month. The music service streams 1.5 billion hours of music every month, which is the equivalent of 170,510 years of nonstop music, and streams 200 million songs before 10 a.m. every day, which is around 8,000 songs per second.

Last month, Pandora played more than 100,000 unique artists and more than one million unique songs, compared to the largest FM radio station in the U.S. that plays more than 270 unique artists and more than 540 unique songs.

“When we launched http://www.pandora.com in 2005, we hoped to create a new way to discover and enjoy music that was completely personalized for each and every listener.  We envisioned a time when artists of all kinds would thrive on radio, connecting with fans who loved exactly their kind of music,” wrote Pandora founder Tim Westergeren in a blog post. “I have to admit, we had no idea what was in store! It has been, and continues to be, an extraordinary experience for all of us.”

As a comparison, competitor Spotify, which launched in the U.S. in July 2011, has 24 million active users and six million paying subscribers globally (one million of which have joined since December).