Approximately 102 million people accessed Facebook exclusively from mobile devices in June, according to a 10-Q document filed with the SEC Tuesday. That marks a 23 percent increase since March, when the social network saw just 83 million mobile-only users. Overall, the company saw 543 million active mobile users in June, 18.7 percent of whom didn't access the site via desktop at all.

In fact, Facebook's active monthly desktop users remained largely flat during the second quarter of 2012, and even dipped slightly across both Europe and the US. The site saw 168 million monthly active users (MAUs) in the US during June — an increase of just ten percent over the same period last year — but enjoyed much stronger growth in emerging markets like Brazil, where its MAUs surged by 146 percent over the year to 54 million. A similarly steep increase was seen in India, where Facebook's MAUs jumped by 84 percent since June 2011, totaling 59 million.

The big takeaway, though, is the apparent migration from desktop to mobile — a trend that could have major implications for Facebook's advertising, which comprised a whopping 84 percent of the company's revenue during Q2 2012.

Recent studies have shown that mobile users tend to spend significantly more time on Facebook than those accessing the site via PC, which would appear to bode well for the company's bottom line. The problem, however, is that Facebook has less ad real estate to sell on its app or mobile site, and has thus far been reluctant to insert more sponsored stories into mobile News Feeds. But if users continue to spurn desktops in favor of smartphones and tablets, the newly public company may be forced to make some changes.