As Microsoft Corporate VP for Windows Phone Terry Myerson and others from Microsoft and Nokia took the stage at the Windows Phone Summit in San Francisco, it’s certain that there were nervous eyes watching the video stream from somewhere in Waterloo, Ontario.

While Microsoft is clearly targeting Google and Apple as its primary competitors with the Windows 8 phone features announced today, the company that has the most to lose with Microsoft’s full entrance into the enterprise mobile business is Research in Motion. Now in fourth place behind Android, iOS, and Symbian in market share, and with Microsoft starting to catch up, RIM was laying off thousands of employees just as Microsoft announced the enterprise-readiness of its next phone OS. And regardless of how rapidly enterprises embrace Windows Phone 8, Microsoft’s other mobile moves could deliver a knockout blow to RIM’s dominance of the enterprise.

BlackBerry phones have continued to be the smartphone of choice for many companies—mostly because of their security and manageability. BlackBerry Enterprise Server was a big reason for that success, giving administrators a huge amount of control over RIM devices. But as more companies have begun to allow employees to bring their own phones and tablets into the enterprise, RIM scrambled to maintain its relevance—especially as its phones lagged in wireless performance, and sales of its BlackBerry 7 phones fell flat.

The company’s answer to that problem was BlackBerry Mobile Fusion, an evolution of BlackBerry Enterprise Server. Last November, RIM moved to make its BlackBerry Mobile Fusion management platform compatible with iOS and Android devices, giving the company a bring-your-own-device play. And in the great purges that followed the departure of RIM’s co-CEOs, new Chief Executive Officer Thorsten Heins made it clear that the company was doubling down on enterprise customers, refocusing on pushing the company’s management platform with corporate customers, while trying at the same time to get them to embrace BlackBerry 7 devices—or at least not jump ship before BlackBerry 10 devices arrive later this year.

But RIM is hardly the only player in multi-platform mobile device management, and now Microsoft is hot on RIM's heels in the big management market too.

Over the past year, Microsoft has been building a strategy that will cement the company’s presence in the enterprise, using its established beachhead with administrators and desktop infrastructure. Since many enterprises that have used RIM’s Blackberry Enterprise Server also have used Microsoft’s management platform (now called System Center 2012), the addition of mobile management capabilities for iOS, Android, and other mobile devices to Microsoft’s Systems Center Configuration Manager makes purchasing a license for BlackBerry Mobile Fusion a bit less attractive—even if RIM’s software is better.

Then there’s Windows Phone 8. When it deploys, it will have the same Windows kernel that runs most enterprise desktops and notebooks, and will be capable of running many of the same applications (with some minor changes). Corporate developers will be able to build native apps for Windows Phone 8 without much difficulty, and the Microsoft Office suite will be available as well.

While Blackberry’s security is well-understood by enterprises, they’ve also invested a great deal in securing Windows—and much of that investment will translate over to Windows Phone 8. And while BlackBerry phones are a favorite of government agencies for unclassified use, most of the classified-use mobile phones used by the DoD are based on a Windows platform—albeit an older one.

All that puts RIM in an increasingly untenable position. With Microsoft’s partnership with (and licensing of technology from) Nokia, its entry into the tablet space, and its deep existing hooks into RIM’s customer base, it’s going to be increasingly hard for the company to keep its grip on corporate IT.

Listing image by Sean Gallagher