Howard Stern’s jump from traditional radio to satellite service Sirius could mark the moment when subscription radio becomes as indispensable to most consumers as cable TV. Or, it could relegate Stern to the fringes of pop culture and have little effect on over-the-air broadcasters. The truth is, no one knows whether Sirius’s gamble will pay off. “The challenge is to train the audience to pay for what they want to hear, uninterrupted by commercials, in the same way HBO trained us to pay for what we want to see, uninterrupted.”