Calling it a "significant milestone," Sirius XM announces it has surpassed the 20 million mark in subscribers, a major achievement for the satellite radio operator. CEO Mel Karmazin says "We have added the last 10 million subscribers faster than the first 10 million -- despite a tremendously competitive environment -- representing a strong endorsement of our service and our programming by discerning consumers who want and demand the best in audio entertainment." This has been a very busy week for Sirius XM. To mark the milestone, Sirius XM will air a subscriber-only broadcast of a Paul McCartney concert scheduled in New York. And, as Radio-Info previously reported, the NFL has renewed their broadcast agreement with Sirius XM for another 5 years, and will also broadcast games online starting next season.