When you've got good news to share, why wait for the next available trading day? Satellite radio star Sirius (NASDAQ:SIRI) revealed yesterday that it had lapped the 6 million subscriber mark on the way to producing its first quarter of positive free cash flow.

The cash flow milestone is a welcome one, even if the company had been pointing to the fourth quarter as a target to achieve it for months now. Rival XM (NASDAQ:XMSR) has made a similar projection. This doesn't mean that either company is actually profitable, though it may help ease fears that the companies are barreling toward bankruptcy.

Closing out the quarter with just more than 6 million subscribers was also not much of a surprise. Sirius had initially expected to watch over as many as 6.3 million subscribers before it warned that it would likely be servicing between 5.9 million to 6.1 million subscribers by the end of the year.

Barring a last-minute miracle from XM, Sirius wound up adding more net new subscribers during every single quarter of the year than its only satrad competitor.

It's not all roses in the Sirius camp, though. Yes, the company landed 2.7 million new net additions for the year as a whole, and that's an improvement over the 2.2 million subscribers it signed up a year earlier. However, that data is front-heavy with most of year-over-year gains coming early in 2006 as Howard Stern took over channels 100 and 101 on the Sirius dial. In the fourth quarter, Sirius landed just 0.9 million net new subscribers after tacking on 1.1 million new listeners a year earlier. In other words, it will be a real challenge to the company's growth rate in 2007.

Yes, Sirius will benefit from a wider range of new cars from companies like Ford (NYSE:F) and DaimlerChrysler (NYSE:DCX) that come factory-installed with Sirius receivers. However, the next wave of adopters are unlikely to be cut out of the same radical commuter mold that saw the value in paying $13 a month for the service. At the retail level, satellite radio has been losing ground to other gadgetry like portable media players and GPS systems since the summer so 2007 will be pivotal year for Sirius, especially if it wants to eventually justify a price hike that will sweeten its profit margins.

Still, kudos to Sirius for hitting two important milestones. Keep going, now, because the road to prosperity is a long one.

For more on this epic battle, check out:

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Longtime Fool contributor Rick Munarriz is a Sirius and XM subscriber but he does not own shares in any of the companies mentioned in this story. 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.