MySpace, the once social networking kingpin that is fast losing traction to Facebook, announced today that it is building an app for Windows Mobile. Microsoft will also open its Adobe Flash-competing Silverlight technology to MySpace Developers.

For Microsoft, this move signifies that they aren’t putting all their eggs in one Zuckerberg-shaped basket. Microsoft previously  invested $240 million in Facebook. MySpace still has more users in the U.S., Facebook is now significantly bigger worldwide.

Facebook may be on an international user-aquisition stampede, the mobile space is still anyone’s game.  MySpace has previously said that it expects to have about half of its traffic come from mobile devices within the next five years. MySpace already has apps for Apple’s iPhone 3G and Android, and the company’s BlackBerry app recently broke download records.

“Our relationship enables app developers to use Silverlight to create engaging MySpace apps and allows Windows Mobile users to have a more personal MySpace experience on their phone,” Aber Whitcomb, CTO of MySpace, said in a statement.