Is Facebook really a mobile company? Facebook finds itself at the front line of the march to mobile. When it burst on to the web in 2004, virtually everyone online was using a computer, be it laptop or desktop. Today, in developed nations at least, we're coming to the point where most of us access consumer online services more often via our smartphones and tablets, and as the leading social network, Facebook is one of the services that hundreds of millions want access to wherever they are. In the developing world, mobile is arguably even more important, as many are skipping computers to go online for the first time via a cheaper device. Facebook offered a watershed moment in its fourth quarter results on Wednesday when it revealed that, for the first time, more members accessed their account via its apps and mobile website each day than via its main website. The growth of mobile is now ringing in significant advertising sales, too. From zero less than a year ago, to 14 per cent of revenues in the third quarter, mobile advertising now accounts for 23 per cent of Facebook's $1.59bn sales. Google, also navigating the migration of users to smartphones and tablets, has a bigger mobile advertising business, but it represents a smaller slice of total revenues. Facebook's rapid progress is therefore undoubtedly worth boasting about, and Mark Zuckerberg and his lieutenants repeatedly returned to their mobile strategy in a conference call with analysts following the publication of the numbers. "More people are starting to understand that mobile is a great opportunity for us," he said. He was keen to emphasise the improvements engineers have made to Facebook's iOS and Android apps, and the generally higher status that mobile now has in the firm. Significantly, Zuckerberg said developers had moved on from simply trying to replicate the main Facebook website on a smaller screen, to working on features that take advantage of the specific capabilities of smartphones and tablets. "What stands out from Facebook's Q4 results is the centrality of mobile for its service strategy and growth," said analysts Ovum. But for all that progress, it remains hard to see Facebook as a primarily mobile service in the same way as, say, Twitter. The migration of its advertising business to mobile is a way behind the migration of its members, as witnessed by the fact it accounted for less than a quarter of sales while serving more daily users than the main website. But Zuckerberg is clearly determined to drive the change through over the next year. Already heavy investment will be ramped up to outpace sales growth in 2013, and some analysts don' believe mobile advertising will be as big a business as on the web, so a year from now investors will expect him to be able to justify his back up his claim that "there's no argument, Facebook is a mobile company." For now, he'll still face a few arguments.