facebook_androidThe App Annie Index for February is out today, and it shows that Facebook has three of the top five non-gaming apps by monthly downloads in the Google Play Store. Its four Android apps are enough on their own to beat out Google’s combined 62 apps in Google Play, making it the top Google Play publisher overall. Perhaps more significantly, though, Facebook Messenger is making a charge, coming in at number four in the most-downloaded Google Play apps that aren’t games, behind only Skype, WhatsApp, and Facebook’s own flagship app.

Facebook is doing fine on iOS, too – there it is the number four publisher, behind Google, Apple, and Out Fit 7. But the more interesting story is over on Android, which is the dominant mobile platform worldwide, especially so in developing countries, where consumers are less likely to be able to afford iPhones. Apple’s iOS, meanwhile, skews heavily towards the US, where different mobile Internet dynamics prevail. The main difference between the US and the rest of the world? The rampant popularity of messaging apps.

As the Wall Street Journal noted yesterday, messaging apps are challenging Facebook for user attention worldwide, but especially in markets such as Japan, South Korea, and India, where Line, KakaoTalk, and Nimbuzz are using chat as a front door to a deeper social experience built for mobile. In China, where Facebook is blocked, Weixin claims 300 million users and is cutting into the popularity of the dominant social network, Sina Weibo. Together, these four apps account for more than half a billion users – not bad, considering only Nimbuzz has been around for much longer than two years.

We’ve pointed out the challenge these apps, which are now effectively social networks, pose to Facebook many, many times. That threat might explain why Facebook was interested in buying WhatsApp, and it could also be one of the reasons it decided to block upstart messaging app MessageMe, which it also apparently tried to acquire. (MessageMe, by the way, was “inspired by” the Asian messaging apps.)

Facebook’s recent moves with Messenger and its high ranking in Google Play, however, suggest it is up to the challenge, even if it so far lags behind its competitors in monetizing mobile chat. The makers of Line, KakaoTalk, and WhatsApp are all in the top 10 for non-gaming apps in Google Play by revenue, according to App Annie, but Facebook Messenger doesn’t yet bring in any money. In response, Facebook is pumping resources into Messenger. Peter Deng, Facebook’s director of product management for communications apps, told the Wall Street Journal that he now spends about 75 percent of his time thinking about mobile messaging. Two years ago, messaging apps were not a big focus, he said. Deng also said that Facebook will accelerate product releases for its messaging services this year, building on the recent addition of audio messaging, video calls, and emoticons.

While the Age of Mobile has made it possible for social networks masquerading as messaging apps to grab hundreds of millions of users while Facebook has played catch up, we are still only at the beginning of this new era. Going by today’s stats from App Annie, it seems Facebook is now as well positioned as any of its upstart competitors to ultimately win in the space – and it is helped in that goal by having 1 billion users already on board. That is potentially bad news for the likes of Line, KakaoTalk, and Nimbuzz. Even though those apps are very popular today, we’ve seen these dynamics play out before on the consumer Web. MySpace and Friendster used to be the dominant social networks in the US, while regional players such as South Korea’s Cyworld and Japan’s Mixi have both fallen to Facebook, despite once being total juggernauts.

It’s difficult to come up with a reason why the dynamics will be any different this time round. While the world is shifting its Web habits to mobile, it is still the Internet, where international borders don’t make sense.

Today, the mobile messaging landscape looks fragmented and messy. It won’t be like that forever. Facebook has already shown that social networking on the Internet is effectively a zero-sum game. Even as it scrambles to counter the challenge from feisty new competitors, it has a fair chance of pulling off the same trick.