Zynga’s acquisition of mobile game developer Newtoy, announced earlier today, is the strongest sign yet of its intention to become a mobile powerhouse. Facebook, despite the launch of new properties like CityVille, is conquered territory; the empire’s attention lies outward.

Traffic numbers always get the most attention when Zynga talks about what it’s doing – in this case, it can claim 12 million downloads for Newtoy’s top game, Words With Friends. But the Words franchise isn’t the most interesting part of the story.

Words With Friends, you see, is a paid app, excluding an ad-supported version, while Zynga is a company whose DNA is built around free apps with in-game microtransactions. The backstory to the Newtoy acquisition is that the company is also the developer behind We Rule, one of the first mobile hits to draw heavily on the Facebook sim game model.

Two months ago in October, Zynga acquired Bonfire Studios, which worked on We Farm, a We Rule sequel. With the two acquired developers in hand, Zynga now has a substantial experience base to recreate its Facebook successes on mobile devices.

It’s probably not a coincidence that We Rule and We Farm were also both published by Ngmoco, which along with its new owner DeNA is being positioned by a number of onlookers as Zynga’s top competitor in mobile.

Zynga has already made a number of key hires for its mobile development efforts, and CityVille, as we pointed out this morning, looks like it was built for mobile release. Our guess is that Zynga is preparing for a turning point in the mobile market, with the intention of recreating the release blitz and resulting explosion in user numbers it enjoyed on Facebook in 2009.

Newtoy will be renamed Zynga With Friends, and will continue to operate out of McKinney, Texas, next door to Bonfire’s Dallas office. The acquisition price was not disclosed.