On the fourth-quarter earnings call, Facebook‘s (NASDAQ:FB) Mark Zuckerberg put things into perspective: “Today there’s no argument. Facebook is a mobile company.”

Hey, remember when Facebook went public back in May, and there was much alarm about its mobile business? Well, that’s a thing of the past. The fact is Zuckerberg has pulled off an impressive transformation.

In Q4, mobile advertising accounted for 23% of total ad revenues, up from 14% in the third quarter. A big part of this came from putting “sponsored stories” in News Feeds as well as getting aggressive with “app install” ads.

But Facebook has also been landing mega-campaigns. For example, a holiday effort with Wal-Mart (NYSE:WMT) resulted in about 50 million add impressions. Michael Kors (NYSE:KORS) also ran a major campaign.

A key to Facebook’s success has been an obsessive focus on engineering. As a result, the core mobile app is now much better — and faster.

Facebook will certainly still face challenges. A major risk is that the company will alienate its users with too many ads. This is especially problematic with mobile devices because of the small screen size (it’s not easy to ignore the ads!).

But on the earnings call, Zuckerberg stressed that he’s focused on making ads relevant and seamless with the experience. And so far, it seems to be working. In Q4, Facebook attracted 680 mobile monthly active users. Oh, and about 157 million of them accessed the service via their mobile devices exclusively.

Zuckerberg also made it clear that his mobile strategy won’t involve building a phone. Let’s face it, the market is already crowded, with fierce rivals like Apple (NASDAQ:AAPL) and Samsung. Even near-dead operators are making comebacks, such as Nokia (NYSE:NOK) and BlackBerry (NASDAQ:RIMM), formerly Research In Motion.

Really, does the world really need another phone?

Probably not. And it doesn’t matter for Facebook. It has plenty more room to find creative ways to monetize mobile. And it could be much more than just advertising. Consider that Facebook has been rolling out various e-commerce properties, such as Gifts. These could provide a nice source of mobile payment revenues.

Then there’s Graph Search. By allowing people to search for restaurants and other types of merchants — with the results based on location information and recommendations — the technology could break into the massive local market. Again, this could be another healthy revenue stream.

For the most part, Zuckerberg is building a mega-mobile platform, which will allow for revenue streams that span across advertising, payments, e-commerce and local. All of these are multibillion markets that are growing at strong rates. More important, with Facebook’s massive traffic, it’s a good bet the company could become a key player in all of these categories.

Tom Taulli runs the InvestorPlace blog IPO Playbook, a site dedicated to the hottest news and rumors about initial public offerings. He is also the author of “How to Create the Next Facebook” and “High-Profit IPO Strategies: Finding Breakout IPOs for Investors and Traders.” Follow him on Twitter at @ttaulli. As of this writing, he did not hold a position in any of the aforementioned securities.