Sirius Satellite Radio reported Monday that it now has more than 4 million subscribers - a 21 percent increase from the 3.3 million it claimed at the end of 2005, writes Media Life (via MediaBuyerPlanner). The company hopes to reach 6 million subscribers by the end of 2006. Howard Stern, who joined Sirius in January, can add his "I Hate Les Moonves" tour to his victories for Sirius; he is considered the major reason for the company's rapid growth. Also, Sirius and several record companies have reached an agreement that will allow Sirius songs to be played on new radio units called Sirius S50 players, which store up to 50 hours of songs for future playback.