About a Quarter Of Facebook Users Connect Via Mobile Phones

Facebook’s quest to become the social operating system of the Web is driven by how many how many other Websites and apps tap into the social network through Facebook Connect. The mobile Web is a big target for Facebook. Back in March, it made Facebook Connect available to iPhone apps, since those are the most fully featured and popular. Today, it took another step in expanding the reach of Facebook Connect to any mobile phone with a Web browser.

Called Facebook Connect For Mobile Web, it will let any mobile site accept Facebook IDs for sign-on, grab social data from Facebook with permission from the user, publish items into their Facebook stream, and more. (Developers can get more details here).

The mobile Web is already a big deal for Facebook. Across all of its mobile apps (iPhone, Blackberry, Nokia, etc), its mobile Website, and SMS, a full 65 million members reach Facebook via mobile devices every month. That comes to 26 percent of the 250 million total active members that Facebook puts out as its official number, or 18 percent of the 370 million monthly worldwide uniques that comScore measures.

Either way it is a significant and fast growing chunk of overall Facebook usage—between a fifth and a quarter. Back in December, only 20 million people were getting to Facebook via mobile devices.