In early 2009, several up-and-coming social game companies were active in iPhone gaming, releasing ports of top Facebook titles for mobile users. Then, as the social companies realized that players weren’t showing up in any great numbers, they mostly turned away from mobile development.

Today, some of those same top companies may be changing their minds again. The one most are watching is Zynga, which was given stage time beside Steve Jobs himself for the June release of FarmVille for the iPhone.

Although Zynga has said nothing publicly about a broader mobile plan, some of its actions do suggest that the company is planning more than just ports of its most popular games — maybe even games designed specifically for mobile.

Acquisitions

In the space of two weeks, Zynga has announced the acquisition of two companies that both have ties to mobile: Dextrose AG, a German HTML5 platform developer, and Bonfire Studios, a Dallas-based game developer.

Dextrose, as we noted at the time of its acquisition, is developing an HTML5 “Aves engine” that the company specifically touted earlier in 2010 as being useful for cross-platform web and mobile. If Zynga intends to stick to the web for most of its games, it’s probably best served by using Flash instead of trying to use HTML5, at least for the near future.

But the standard, which will work as well on Android or an iDevice as on an ordinary browser, could offer possibilities to develop a game just once for both web and mobile platforms, instead of going back for a later port as Zynga did with FarmVille. For now, most developers still wouldn’t consider this process straightforward, but Zynga may see greater possibilities in the Aves engine; we’ll have more on this later.

Bonfire Studios is a less clear case, because the company worked on titles owned by other companies. One its few known projects, however, was Ngmoco’s We Farm, an iPhone title with a clear connection to FarmVille. Ngmoco is the best-known name in the social mobile space, so Zynga’s buyout of Bonfire three months after the release of We Farm was probably not coincidental.

In August, Zynga also bought Unoh, a Japanese developer with well known social-style games on Japan’s mobile social networks.

Hires

With more than 1,200 employees, it’s hard to tell exactly how many people Zynga has hired who have a mobile background. The company only loosely refers to its mobile gaming plans, like when it participates in Apple launch events, or when it makes new executive appointments, as with its appointment this week of former Yahoo exec David Ko as its head of mobile.

At other times, Zynga has been seen advertising to fill Android development spots, mobile product management and interface roles. Right now, the company has at least two mobile engineering roles open in San Francisco.

Investments

Zynga’s acquisition of Unoh in August was not completely out of the blue; the two companies may have been connected through Softbank, the Japanese conglomerate that invested $150 million in Zynga in July.

While Softbank and other Japanese firms have hopes of interesting Japanese gamers in web-based games, the country’s hot business is in mobile. It’s difficult to see why Softbank would have invested such a large sum without some expectation that Zynga would go into mobile, at least in Japan.

Still, for now the best evidence of a Zynga strategy to become a true multi-platform developer remains circumstantial, though we believe it intends to progress down this path. The first full view of Zynga’s plans may not come until the company is ready to release a new product — something it has been slow to do throughout this year, even on the web.