(Business 2.0) – If there were doubts about satellite radio's mass appeal, this year they disappeared. In January a mere 1.6 million people pulled down music and other entertainment from the sky. But by year's end, total subscribers to services offered by XM Satellite Radio and Sirius Satellite Radio will top 4 million. At an average of $10 per month per subscriber—plus new subscribers paying about $150 for electronic gear—satellite radio is now a market worth $840 million annually. Automakers like GM and Honda have heavily promoted satellite radio, and big demand for reception gear is expected this holiday season. The medium's most significant affirmation, however, came from Howard Stern, one of broadcast radio's biggest moneymakers. Facing the wrath of the Federal Communications Commission and censorious Clear Channel Communications for the content of his nationally syndicated show, Stern threatened to defect: not to Canada, but to satellite radio. — MICHAEL V. COPELAND