Virtual farming games have taken over on social networks in Asia, and on Facebook around the world, but now they’ve also come to Apple’s iPhone. PlayMesh, the maker of iPhone app iMafia, has a new one out: iFarm. The simple farming simulation launched on November 20th, and has already reached the #1 spot on the iTunes App Store free apps list.

It’s not clear exactly why, although one can imagine that the success of Slashkey’s FarmTown, Zynga’s FarmVille, and the range of other titles on Facebook have made many iPhone users aware of the game concept.

And, iFarm could use a couple features if it hopes to get as big or as lucrative as farming games on social networks.

In terms of virtual goods, there’s the usual farming dynamic of growing crops, selling them, buying farm decorations, etc. However, the company has not yet integrated Apple’s new free-to-play virtual goods payment system. Instead the game relies on what iMafia pioneered on the device — to buy more points, you actually purchase a for-fee version of the iFarm app, or you install a free version of another one of the company’s many other gaming apps. That is a clever kludge, but still not as elegant as just being able to click a button and charge a dollar to your iTunes account.

And in terms of social features, the game does include an option to find friends, but it’s pretty rudimentary. You need to click into a settings menu, click on “Friends” then type in the name of a friend in the game. For new users, there’s no easy way to see existing friends. Farming games on social networks have made social relations a much more central feature. You can do thinks like be “neighbors” with a friend, then go visit their plot of virtual land, pull some virtual weeds, and get points. This interface seems like a great opportunity to integrate Facebook Connect for the iPhone, especially when you consider the tens of millions of Facebook users who are already obsessed with virtual farming.

Meanwhile, we also have to wonder when Zynga or other social farming game developers will port their existing games to the iPhone and compete with iFarm head on. The history of social gaming shows that the sort of success that iFarm is seeing now, er, inspires competitors to come out with similar games.

However, the larger question for potential iFarm rivals is if the iPhone platform offers as much potential business as Facebook and other social gaming sites. So far, most big social game developers on Facebook and MySpace have kept most of their efforts focused on those sites.