Eyes 20 million subscribers by 2010.

XM Satellite Radio passed the 4 million subscriber mark––adding its latest million in fewer than five months. It took 23 months for XM to reach its first 1 million subscribers and eight more months to reach 2 million. Six months later, the satcaster hit the 3 million mark.

The company says it is on target to total 5.5 million subscribers by year-end 2005. Its long-term goal is to convert some 20 million by 2010.

XM claims that it has acquired 4 million subscribers in less time than it took cable TV, CD players, MP3 players, cell phones, personal computers, local radio or broadcast TV to reach critical mass.

XM competitor Sirius Satellite Radio claimed 1.5 million subscribers at the end of March 2005.