Remember the Kin, Microsoft's billion-dollar bet on the future of phones?

The Kin was supposed to show the world that Microsoft could re-think mobile design for the social media age. Instead, it reinforced the perception that the software giant couldn't do much more than watch the mobile market slip away, no matter how many billions it spent.

Well, now Microsoft has spent another $7 billion on what it sees as the future of mobile, snatching up Nokia's smartphone business and licensing its accompanying patents. But this new Microsoft-backed phone-making giant (Microkia?) creates a big problem for Windows Phone that could see it tumble into the dustbin of history, much like the Kin.

The problem is this: Why on Earth would a handset maker – Samsung, for example – pay Microsoft for an operating system, when it can get one for free from Google? That free OS, Google Android, even includes the source code, which any handset maker can modify and reuse – at least to a certain extent.

>'You need to use all available tools. Phones and devices are ground zero for tinkerers and modders' Sam Ramji

Since releasing Android in 2008, Google has shown that a well-managed open source alternative can take market share from established players like Apple and Blackberry in the smartphone market, in large part because it's free. And Microsoft's smartphone business isn't all that established at the moment.

But there may be a solution to this problem. Microsoft makes less than $10 per Windows Phone license, so it's already a fair bit nearer to free than the Windows operating system it sell for PCs, an OS that can cost dozens of dollars per copy. So when Steve Ballmer's successor takes the reins a year from now, maybe he should consider a bold new strategy. Why not open-source Windows Phone?

When Sam Ramji worked at Microsoft back in 2007, he thought the company should do just that. In fact, he and his open-source strategy team recommended it to Microsoft. With a negligible marketshare, "you need to use all available tools," says Ramji, now vice president of strategy at developer tools vendor Apigee. "Phones and devices are ground zero for tinkerers and modders." And they love open-source.

But Microsoft rejected Ramji's idea, and instead spent $1 billion on the Kin. We know how that turned out. And, since then, Microsoft has gone through many other changes that would make it easier for the company to open source Windows Phone.

First and foremost, there's Nokia. Microsoft is now a full-fledged hardware player that can make money by selling handsets. Also, the company doesn't hate open-source as much as it once did. It has shipped lots of open-source code for its Azure cloud platform, and even contributed to the Linux kernel.

An open-source Windows Phone could evolve more quickly – in theory at least – and it could be easily hacked to power new devices and accessories. So it's possible that the company's new CEO might even see a bigger role for it in a re-invented Microsoft.

If Microsoft is making money from Nokia phones and the apps that run on top of them, an open-source Windows Phone operating system makes an awful lot of sense. "They could take a page out of Google's book and recast themselves as a hacker-friendly company," says Ramji.

Over the past several years, Microsoft has shown itself to be remarkably adept at following Google. So what's one more time?

But there's a big catch. Five years ago, Microsoft's desktop and mobile operating systems were separate beasts. But that's changed as the company has sought to unify Windows across all devices. "Now it seems that Windows, Surface, and Windows Phone all share a lot more code than they did back then, so there may be no way to open source the phone without opening the crown jewels," says Ramji.

Microsoft has many ways of protecting Windows, even if it were to open source part of the code. It owns the trademark, and it has a massive patent portfolio at its disposal, too. But this is Microsoft we're talking about. Huge Windows profits let Microsoft do things like $40 billion stock buybacks, so if it felt that there was any chance it could lose control of its fat Windows profit margins to a bunch of clones, then open-sourcing Windows would be a non-starter.

"The power of open source can work both ways. It can work to your benefit, and it can work against you." says Bill Hilf, the open source guru who hired Ramji at Microsoft and now works for another tech giant, HP. Open sourcing Windows Phone might win new partners for Microsoft, he says, but it could just as easily allow companies to compete with Microsoft – using its own code.

For this reason, Microsoft is unlikely to open source Windows Phone. Some things never change – and that's too bad. "The good will companies get from open source is priceless," says Al Hilwa, an IDC analyst who follows the company. "And Microsoft can use all the good will it can get."

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Cade Metz contributed to this story.*