When Nokia announced Tuesday morning that it would not only buy the rest of the Symbian mobile operating system, but also make it available for free and eventually open source it under the Eclipse Public License, there's no doubt competitors took note. Despite a smattering of applause from the Linux camps, there's no indication that any are ready to cede even more market share to the market leader.

"What it really means is that we're at an early stage of a full scale war for becoming the next development platform for mobile devices," Jim Zemlin, who runs the Linux Foundation, said in an interview. "This stuff tends to winnow out into a few winners. Symbian is upping the stakes, offering its platform for free in order to draw more people into their alliance. These alliances are often self amplifying."

If nothing else, Nokia's moves to make Symbian a free and open mobile operating system should put pressure on the company's competitors to keep innovating and giving customers -- device manufacturers, consumers, and carriers alike -- what they want. Nokia said Tuesday that it aims to make Symbian -- already the top smartphone operating system -- the "most widely used software platform on the planet."

For its part, Microsoft is standing firm. Unlike Nokia's strategy for Symbian, Microsoft Windows Mobile remains a proprietary mobile operating system that costs money. It costs to put Windows Mobile on a smartphone, and Windows Mobile can't just be altered willy nilly. However, in exchange, Microsoft co-markets Windows Mobile phones as a way to drive sales for handset manufacturers and mobile carriers.

In an interview, the company attempted to minimize the challenges a free, open source version of Symbian represents and maximize the potential challenges Symbian itself faces. "In the short term, it doesn't seem like it's such a change," Scott Rockfeld, group product manager for Microsoft's mobile communications business, said in an interview.

It's unclear whether device manufacturers will want to continue paying high fees for Windows Mobile license when the market leader suddenly cut costs to zero. Over the longer term -- by 2010, Nokia says -- Symbian will become open source and throw its doors open to developers, including a malleable user interface, and addressable low level code, in ways that Microsoft can't approach.

However, Rockfeld cited projections that Windows Mobile will have sold 20 million licenses by the end of the year, a more than 100% growth rate year over year, as well as the fact that there are more than 18,000 Windows Mobile applications now floating around, as evidence that Microsoft has a sustainable business model. "Developers are in Micorsoft's DNA," he said.

Another familiar line of argument: Microsoft can make Windows Mobile a part of a larger, integrated experience, leveraging its desktop user base to make Windows Mobile more compelling to consumers. The company has said that going forward, Windows Mobile, Windows, and Windows Live will be increasingly connected or easy to connect.