Mary Jo Foley has uncovered a March 11 Nokia filing with the SEC in which the company spells out some details of its plans to move to Windows Phone. It’s interesting reading.

Nokia filed on March 11 a form 20-F with the Securities and Exchange Commission which mentions a number of new tidbits about Nokia’s smartphone-centric partnership with Microsoft.

(A PDF of the nearly 200-page document is available on the Web. If you have problems viewing that one, here’s another download link.)

The document confirms that Microsoft and Nokia still haven’t finalized the deal, announced in February, noting the pair has “entered into a non­binding term sheet… (while) the planned partnership with Microsoft remains subject to negotiation and execution of definitive agreements by the parties.”

There’s been some debate as to whether Nokia will be fielding its first Windows Phone 7 devices in 2011 or 2012. (The last “official” word from Nokia was the company expected to start selling WP7 phones in volume in 2012.)

But in the 20-F, Nokia officials said the transition to Windows Phone as its “primary smartphone platform” will take “about two years.”

Nokia officials called out 2011 and 2012 as “transition years,” during which the company will be moving to Windows Phone and investing “in building a new ecosystem with Microsoft.” The ultimate goal is to try to “retain and transition the installed base of approximately 200 million Symbian owners to Nokia Windows Phone smartphones over time,” the document said.

A couple of other details uncovered in this document:

• Divisions of labor. “Nokia would bring assets such as its brand, hardware, productization, global reach, application store, operator billing support, maps and location­-based assets to the partnership. Microsoft would bring their next generation smartphone platform with Windows Phone, as well as search, broader advertising, ecommerce, gaming and productivity assets such as Bing, AdCenter, Xbox Live and Office.”
• Silverlight rules. “By leveraging Microsoft’s proven developer tools and support, based on Silverlight, with our operator billing, merchandising and global application store, we intend to offer new monetization mechanisms for developers while providing access to Nokia’s global scale.”