A natural question is whether Blackberry's BBM messenger service has been overlooked and deserves a big valuation of its own. The entire company, which has seen a dramatic sales decline as consumers switched to Android and Apple devices, has an enterprise value of just $2.9 billion.
That suggests investors ascribe very little value to the 80 million active BBM users BlackBerry last reported. Were they worth $42 each, BBM would be worth $3.4 billion, which would come on top of other valuable assets Blackberry has, such as government customers who will likely stick with the service, and a bundle of patents. BlackBerry declined to comment.
There is some reason to believe BBM has more value than the market reflects. After all, BBM was once the dominant messaging service. It lost that crown as users abandoned BlackBerry devices in favor of other phones, which didn't allow them to use BBM until BlackBerry introduced it on other plaforms last year.
No doubt, some users are returning to BBM. BlackBerry said in late December that 40 million users had registered BBM on Apple and Android platforms in the prior 60 days.
But keeping that kind of momentum will be tough. Many users who once used BBM on their BlackBerry devices are now completely comfortable with a network of contacts on WhatsApp. Tim Long, an analyst with BMO Capital Markets, estimates that BBM's user growth lags far behind WhatsApp's clip of about a million per day.
And any real attempt to catch up would be an expensive pursuit for BlackBerry. The company will lose $1 billion in free cash in the year through February and $800 million in the year through February 2015, according to consensus estimates.
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Burning more cash would be a very difficult maneuver for Blackberry as it fights sales declines in its other businesses. A rival like Facebook, meanwhile, will happily pour loads of cash into WhatsApp without worrying about making any immediate return. Investors who own BlackBerry now are probably more focused on the company's return to profitability, which it acknowledges is years away.
Even so, BBM's user base could have value to another company that's not afraid to invest in it. Many of BBM's users are in emerging markets where BlackBerries themselves are still common and there's still a chance to migrate users onto new phones.
Who might take interest? One possibility is a mobile carrier in regions where customers often use messenger services like BBM instead of traditional text messages. The likes of Singapore Telecommunications or Telefonica could see BBM as an opportunity to regain control of customers who rarely use their voice or text services, said James Citron, founder of Outspoken, a U.S. firm that offers messaging services for companies including Cox Media Group and Jack in the Box.
Given its questionable growth prospects, BBM probably isn't worth the $42 per user that WhatsApp just received. And Blackberry itself isn't likely to turn it into a revenue producer anytime soon. But if the right buyer shows up, BlackBerry investors should welcome a couple of billion dollars in the company's pocket.
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—By CNBC's John Jannarone. Follow him on Twitter @jannarone