I've been a happy customer of XM Radio for two years, and I'll be even happier when I can access the full suite of channels offered by XM and Sirius on their merger. Many don't think the merger will get through. The FCC has an explicit rule prohibiting joint ownership of the spectrum. A narrow definition of the relevant market for antitrust combination analysis would yield an HHI score off the charts (i.e., if the relevant market is satellite radio, the merger yields a monopoly). Despite all that, my prediction is that the merger gets through.
XM and Sirius face competition from all sorts of fronts, from traditional (free) radio to iPod link-up. While some of these might not be considered "substitutes" for antitrust analysis purposes, there's no question that terrestrial radio - and nascent high-definition radio in particular - will be considered. Layered on this competitive analysis will be the fact that two satellite competitors, with their astronomical cost structures, are probably not viable long-term anyway. This will take care of the DOJ's concerns. The FCC will do a similar analysis, and reach the same conclusion and eliminate the spectrum cross-ownership rule, although it will likely be a more tortured path getting there than that of DOJ.
Is many respects, the current FCC prohibition is akin to the cellular cross-ownership rule, which prohibited the same entity from owning both cellular licenses in any given geographic market. That rule was eliminated about four years ago as the availability of PCS spectrum made it largely moot. Circumstances demand a similar result here.