When a money market fund's net asset value slips below the fortressed $1.00 mark, it's called breaking the buck.

However, for some stocks, the dollar bill is more a ceiling to crash through than a buckling floor.

Given the heady momentum at Sirius XM Radio (NASDAQ:SIRI), it may not be long before shares of the satellite radio operator crack the $1 mark. The stock traded as high as $0.95 this morning, putting it a good push away from pricing itself to the left of the decimal for the first time since September 2008.

Everything seems to be going the company's way these days, after capping off a roller coaster of a year in 2009, with the resumption of subscriber growth, free cash flow generation, and credit rating upgrades.

It's been even sweeter just a single month into 2010, as even cynical analysts have hopped on the bandwagon.

The revival at Ford (NYSE:F) has played a major role in Sirius XM's recent gains. The automaker posted a surprising 25% spike in January sales, fueling expectations that roughly half of the owners of those cars with factory-installed Sirius receivers will eventually become paying subscribers.

Breaking through the buck's ceiling won't just be a round milestone. Nasdaq is delisting companies that can't get out of the penny stock muck -- and Sirius XM has been under the shadow of the exchange's delisting notice since last summer.

Hitting the $1 mark will be a huge achievement for a company whose stock was trading for as little as $0.05 a share nearly a year ago.

However, this doesn't mean that Sirius XM was ever a penny stock. On an enterprise value basis -- once you factor in the roughly $3 billion in debt and Liberty Capital's (NASDAQ:LCAPA) 40% preferred share stake -- you have a company that is currently worth about $9 billion.

DirecTV (NYSE:DTV) and Dish Network (NASDAQ:DISH) weigh in at $34 billion and $12 billion, respectively, but satellite television ransoms are several times what mainstream audiences will pay for premium radio.

DirecTV and Dish Network are also profitable, but that is a club that some analysts see Sirius XM joining as early as this year. Improving margins, growing audiences, and expanding what consumers are willing to pay for premium audio are the keys for Sirius XM to build on once it hits the $1 mark.

It's almost there, as crazy as this all seemed a year ago when Liberty Capital and EchoStar (NASDAQ:SATS) seemed to be the only outside parties with the means to keep Sirius XM out of bankruptcy reorganization.

It's been a great 12 months for Sirius XM -- and it still has a dollar bill to break through.

Now, I do hope I can interest you in taking the Motley Poll below and then scrolling further down to share your thoughts in the comments section?

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Longtime Fool contributor Rick Munarriz is a subscriber to both Sirius and XM. He does not own shares in any of the stocks in this article. He is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance. The Fool has a disclosure policy.