One of last week's grim shockers is that Vonage (NYSE:VG) shed 14,700 net subscribers during the fourth quarter.

Sure, Mr. Market has taken Vonage out to the alley and bloodied it up in the past. Whether it's the Internet phone service provider's lack of profitability or boneheaded blunders, Vonage didn't accidentally stumble into the penny stock muck. However, at least Vonage could always point to its sequentially superior headcount as a silver lining. As long as the service was gaining in popularity, all of its other shortcomings would have a chance to fall into place.

No more.

Is Sirius XM Radio (NASDAQ:SIRI) now walking a mile in Vonage's moldy shoes?

Like Vonage, Sirius XM is a company that has grappled with profitability. It is also a stock that is trading for pocket change. The only thing it would need is a declining subscriber base to complete the outfit. That mirror may roll out on March 17.

I'm giving you two weeks to get ready
Sirius XM issued a press release this morning, delaying the filing of its annual report. The company will now discuss its financials for the final quarter of 2008 on the morning of March 17. Shareholders, start fretting.

One can argue that Sirius XM has already set the bar low enough to clear it with ease. It hosed down its guidance back in November, when it projected a total of 19.1 million subscribers by the end of 2008. The target was a loftier 19.5 million subs just two months earlier. The company closed out the third quarter with 18.9 million members on its rolls, so how hard can it be to activate 200,000 receivers more than it shuts off for those who cancel?

Well, have you seen the sorry reports coming out of Ford (NYSE:F) and General Motors (NYSE:GM) lately? New cars aren't exactly flying off the lots these days, and that's huge for Sirius XM because the company's retail subscriber base -- consisting of the accounts that aren't being hooked up with Sirius or XM through factory-installed car systems at the showroom -- is already falling. Through the first nine months of 2008, Sirius XM shed 202,291 net retail subscribers.

How confident can you be that Sirius XM will hit the 19.1 million subscriber mark when it reports in two weeks? Even if it does, it would be a shock to see it stick to its earlier projection of gaining 1.5 million net new subscribers through 2009. From September to November, that target went from 21.5 million to 20.6 million. You would be living in a cave if you haven't noticed the economy deteriorate in recent months.

Oh, and if you were living in a cave, your satellite reception would be lousy.

Only Subway is moving subs these days
These haven't been fun times for subscriber services. For every Netflix (NASDAQ:NFLX) that is growing its user base, you're finding companies like DISH Network (NASDAQ:DISH), Vonage, and SprintNextel (NYSE:S) going the wrong way. All three of those companies have chimed in over the past few days with net subscriber losses in their latest quarterly reports.

Since Sirius XM has scheduled its conference call just two weeks before the end of the current quarter, it should have excellent visibility in updating shareholders on its first-quarter guidance. My prediction is that it manages to stay barely positive in gaining subs during the fourth quarter, but warns that it will lose net subscribers during this year's first quarter. At the very least, expect it to come in way off its target of 20.6 million total subscribers by the end of 2009.

Between the crummy economy, lack of new car sales, and Sirius XM's recent rate hikes how can anyone realistically expect anything else?

It obviously wouldn't be the first subscriber service to get sliced in this economic meltdown, but it won't be able to make any more Vonage jokes after that.

Some other Sirius stories:

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Longtime Fool contributor Rick Munarriz is such a fan of satellite radio that he subscribes to both Sirius and XM. He does not own shares in any of the stocks in this story, save for Netflix. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.