Pandora CEO Tim Westergren reports that the social music service has reached the milestone of 2 million iPhone users:

At 10:04am this morning we hit 2,000,000 registered iPhone Pandora users!

We’re hearing all sorts of wonderful feedback from listeners who are using it on their commute, jogging with it, plugging it into home audio systems…you name it. And as usual, offering all sorts of great feedback and suggestions. It’s thrilling for us to see the broader vision for Pandora take shape. Our hearty thanks for your continued support and input.

It also makes us very happy to know that the 60,000+ artists in our collection are now getting played on car radios all across the country. Times they are a changin’ …

This is an impressive milestone for Pandora, but also highlights the growing importance of the iPhone as a platform for social media applications.