IT LOOKS AS THOUGH THE MERGER of XM Satellite Radio and Sirius Satellite Radio might happen, after all. In the past month, Sirius shares (SIRI) are up 24% and XM's (XMSR) are up about 25%. Terms of the agreement announced earlier this year call for XM shares to be exchanged for 4.6 Sirius shares; XM is now trading at about a 9% discount, much less than earlier in the year. Several Street analysts in recent weeks have predicted that the deal will soon win approval from both the Federal Communications Commission and the Justice Department. What once looked like a deal that would never make its way through the Washington bureaucracy is increasingly looking like one that will happen soon. And that's when we learn whether satellite radio will really work, long-term.