In its latest social acquisition, Google has bought mobile game developer SocialDeck, according to a letter posted by the company. SocialDeck is located in Waterloo, Ontario, close to a regional Google office.

SocialDeck’s games were downloaded about a million times in 2009. Its games include Shake & Spell, Color Connect and Pet Hero.

What makes this more interesting than just a game developer acquisition is that SocialDeck has significant cross-platform experience. A non-game product it offers, called Spark, provides social integration across Blackberry, the iPhone and Facebook, while Shake & Spell also works on all three of those platforms.

Google’s gaming interest is obviously with Android. But it’s also reportedly working on a social platform to rival Facebook; Google’s technology plans could be advanced by SocialDeck’s experience in extending the social experience across multiple devices.

Buying SocialDeck also seems to fit in with Google’s broader plans, which we wrote about following its acquisition of Slide. With Slide, Google is likely working on a broad, viral platform for both the web and its own mobile devices.

The effort is being headed up by Slide founder Max Levchin, as we reported last week; it’s possible he had a hand in buying SocialDeck, although the timing may have been too close.

As for SocialDeck’s team, founders Anish Acharya and Jeson Patel came from Amazon and Microsoft, while CEO Dan Servos was formerly head of casual and social game developer NeoEdge.

There’s no word yet on how much Google paid for SocialDeck. The company had raised $250,000 from the Blackberry Fund in 209.

The text of the letter:

SocialDeck is joining Google!

Big news! We’re super excited to announce that someone found our social games as fun as you have — in this case, that “someone” is Google. SocialDeck has been acquired and we’ve joined the Google team.

We started this company with the goal of connecting friends through social games on all kinds of exciting mobile devices. We’ve been amazed and humbled by all the stories and experiences our customers (you!) have shared with us.

Thank you for all your support and for being part of SocialDeck’s success so far.

Happy Shaking!

– The SocialDeck Team