Owners of compatible BlackBerry Tour, Bold, Curve, and Storm smartphones can now stream Sirius XM Radio (NASDAQ:SIRI).

It's been several months since the launch of its official application through Apple's (NASDAQ:AAPL) App Store, so it was really just a matter of time before Sirius XM reached out to Research In Motion's (NASDAQ:RIMM) larger smartphone audience.

Investors should temper their enthusiasm over the news -- and the reason why has nothing to do with premium audio streaming likely being a harder sell to the corporate crowd of BlackBerry enthusiasts.

This morning's press release liberally sprinkles the word "free" in its release -- it appears four times before you've even finished the second paragraph -- but the app's not exactly a freebie. Even existing Sirius and XM subscribers have to pay a premium to receive online streaming, a demand that has kept the popularity of the satellite radio purveyor's iPhone and iPod touch app in check.

Despite quickly topping 1 million downloads through Apple's virtual storefront, the app's number of actual paying customers was initially uninspiring. CEO Mel Karmazin kept euphoria in check this past summer, when he warned that App Store subscribers "should not be a significant number" at the time. Until we get hard numbers or a public sentiment shift -- or see average revenue per user spike -- it's hard to consider these pay-for-streaming apps as serious pieces in the Sirius XM mosaic.

The satellite-radio giant is still at the mercy of automaker installations, which is actually a good thing these days. Ford (NYSE:F) sales have been spiking in recent months. Even this week's Toyota (NYSE:TM) scare could be good for Sirius XM, if it prompts Toyota owners to trade in their cars for new rides.

There may come a time when factory receiver installations in new cars will need an assist from premium streaming applications to boost Sirius XM's subscriber count, but it's clearly not necessary now.

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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 companies in this story. 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.