I don't think is a prima facie case of a monopoly at all. In order to define it as one you have to approach it as a very narrow market (ie. satellite radio). I would suggest the market is actually defined by a means for delivering content to people. XM and Sirius radio's true competitors are commercial AM & FM radio, CDs, podcasts, and silence.

Its like the Coke CEO who told a shocked crowd that their biggest competitor wasn't Pepsi, but was actually water.

i was going to write what Hank Porter did, so just to keep dana from being confused about this in the future, i second mark porter completely: it is not an obvious monopoly in the slightest. i have an enormous variety of choices other than satellite radio, which, other than at the place where i get my hair cut, i have never listened to.

from what I've read, it is HIGHLY unlikely that the FCC will go against the DoJ to block the merger.

I'm going to go with the Standard Oil Trust as a more obvious instance of monopoly. Just for fun, I'll also throw out Carnegie Steel, Microsoft, IBM and AT&T.
I'd like to add my support to the previous comments. You would have to be looking at XM's and Sirius's market in a very artificial and narrow way to conclude that their combination would result in a monopoly.

Well, I know there are "natural competitors" to satellite radio...terrestrial radio, iPods, singalongs, whatever. But, truth be told, I don't really buy the argument that the competitive landscape has changed THAT dramatically since these guys were given their licenses and FREE SPECTRUM) in the 1990's.

What people tend to forget is that when these licenses were granted, the two licensees specifically pledged not to merge...that was the price they paid for getting spectrum that would have cost $10's of millions had they had to buy it at auction. Now, a decade later, they've overspent by bidding billions for exclusive rights to NASCAR and Howard Stern and a bunch of other crap, and they find the business isn't as insanely profitable as they'd hoped. So what do they do? They renege on their promise not to merge. And they argue (laughably, IMO) that it was IMPOSSIBLE 10 years ago to see the changes in the competitive landscape that have raised the barriers to survival absent a merger. And they PROMISE (really, really, really) that they won't abuse the monopoly power they have over their free spectrum by raising prices now that they've eliminated competitition.

Just my view.

I agree XM & Sirius should be penalized for reneging on their promise. But they're not a monopoly - I have an iPod, why the hell would I pay a monthly subscription fee to hear mostly lame radio stations that have programming inferior to my iPod? And then there's competition from the internet - as more and more web friendly devices come on the market making it possible to listen to streaming audio in your car I think subscription satellite radio will be either be doomed or have to dramatically lower its pricing.