On Sunday we anticipated that Microsoft would start talking more about Windows Phone 7.8 as all signs point to January 31st as the beginning of a global rollout for current Windows Phone users.

Today, Microsoft has announced the Windows Phone 7.8 SDK update, which will allow developers to better target the 7.8 changes—specifically new Tile options—and to make sure that the apps behave as intended.

Detailing the update on the Windows Phone Developer blog, Microsoft’s Cliff Simpkins explains why devs will want to download this and get their apps updated as soon as possible.

The main new features for Live Tiles are the following for 7.8:

  • The app’s primary tile can have a customized small tile, support wide tiles, and also take advantage of the Flip tile template.
  • Secondary tiles can be enabled to take advantage of all three of the new tile templates (Flip, Iconic, and Cycle).

Apps updated for 7.8 will of course still run just fine on Windows Phone 7.x, meaning this won’t “lock out” users, it simply adds more features much like how Mango added new options when it was released.

The bad news is this SDK does not add any new APIs to 7.8. That means outside of some tile behavior we don’t expect to see lockscreen support besides the official Bing image-of-the-day, which is native to the system.

With the news of the SDK coming out, we’re quite confident now that the 7.8 OS update is right around the corner. Though it may take a few weeks or even months for individual carriers to sign off on the update, at least the process will have begun.

Developers can read in more detail about the 7.8 SDK here on the Windows Phone Dev blog.