Microsoft has welcomed the transformation of the Symbian mobile-phone platform into an open source project, because the software giant contends the change will create a host of new problems for the Symbian community.

"They're opening themselves up to some of the same challenges of all open source projects," says Scott Rockfeld, group product manager for Microsoft's Mobile Communications Business.

Rockfeld sums up those challenges with what some might call the "F word": fragmentation. Fragmentation is bad, he says, because application software developers have to create multiple versions of their code for different operating systems, or different versions of the "same" operating systems. "There are more Linux consortiums that come and go than there are Linux phones," he says.

The comment may be a bit misleading, because the Symbian operating system is not Linux based. It's a proprietary, micro-kernel, embedded operating system, and one of -- if not the -- leading mobile-phone systems software in the world. It's the heart of Nokia's widely used S60 software platform, used by Nokia but also licensed to other handset makers, such as LG Electronics and Samsung.

What's changed is that Nokia, in agreement with its partners, bought the remaining outstanding shares of the Symbian joint venture, then turned over the Symbian operating system to a new, open source entity: the Symbian Foundation. The challenge is whether the foundation can create and sustain a viable and vital community of developers for the operating system.

There's even a bit less fragmentation in the Linux realm. The Linux Phone Standards Forum (LiPS) has just announced it will merge into the LiMo Foundation, an industry group that's developed a full, Linux-based mobile-phone software stack as an alternative platform to Symbian and Windows Mobile.

Microsoft doesn't believe in the F-word, Rockfeld says. Instead, the company has what he describes as an "open platform" in Windows Mobile. "We mean that the platform is open to anyone who wants to build on it," he says. In Microsoft's definition, "open platform" means a proprietary operating system, the development of which is completely and tightly controlled by Microsoft, and that is accessed via some 120 documented APIs available to application developers.

Microsoft recently released Windows Mobile 6.1, and the first mobile phones to use it are just starting to appear. Cellular chipmaker Qualcomm sees a role for the future Windows Mobile 7 in a new class of mobile devices: "mini-notebook" or (perhaps) "supersmartphone" PCs, compact computers with 7-to-10-inch screens and Internet connectivity over 3G cellular networks.

The Windows Mobile software developers kit has been downloaded 3 million times; and in a few weeks, at the close of its current fiscal year, Microsoft will have sold almost 20 million Windows Mobile licenses during the past 12 months, Rockfeld says. "If developers want to build a Windows Mobile application, it will run consistently on all 140 [currently existing] Windows Mobile devices," he says.

Microsoft makes it easy for handset makers and mobile carriers because Microsoft does all the heavy lifting with regard to the underlying software platform, which it willingly tweaks to tailor a specific phone and its user interface to a manufacturer's or carrier's requirements, Rockfeld says.