GeekWire reports that Joe Marini, principal program manager for the Windows Phone web platform, is no longer employed at Microsoft. Marini had been at Microsoft since 2003, and was most recently seen giving a public talk at Microsoft’s BUILD conference in Anaheim last week.

News of Marini’s departure arrives after he posted numerous tweets regarding an unreleased Nokia phone sporting Microsoft’s mobile operating system. A company spokesperson declined to make any comment about his departure, citing a policy against discussing personal matters.

But people within the Redmond company are claiming that he resigned after learning company plans to let him go for improper use of social media and disclosing confidential information. According to Microsoft’s social media and blogging policy (PDF), employees are supposed to “be smart” and not dump information into tweets or posts that could be considered confidential… like an unreleased Nokia phone.

“I just got a chance to try out one of the slickest looking #Nokia phones I have ever seen. Soon, you will too! #wp7,” he tweeted on September 7. Not stopping there, he decided to actually rate the device with a firm ’8′, saying that it had a solid feel, a good camera, a responsive UI and nice little touches on the body construction. So far, the phone sounds like a slick device.

But rating your unreleased product probably isn’t a good idea. Explaining why your product didn’t score a 9 or 10 probably isn’t the best promotional tool either, and likely a good reason to receive a swift kick out the door. “The camera was good, but I didn’t have optimal lighting,” he responded when asked why the device only scored an 8. “I’d like a larger screen too.”

Marini’s outing is reportedly part of Microsoft’s full-frontal attempt to curb leaks. The company recently kicked out one journalist from the BUILD conference for breaking an embargo by prematurely posting video content about the upcoming Windows 8 operating system.