• by Mark Walsh  @markfwal, December 23, 2013

A few years ago, Facebook launched a mobile service called Facebook Zero, providing free access to a simplified version of the social network, mainly for those in emerging markets who lack data plans. The company has also partnered with overseas carriers toward the same end.

Now T-Mobile is planning to offer free Facebook access in the U.S. to customers even if they don’t have monthly data plans.

In an update to its GoSmart Mobile prepaid wireless service, the No. 4 U.S. carrier will throw in free use of Facebook and Facebook Messenger starting in January. Customers who choose GoSmart’s $25 per month talk-only plan or its talk and text plan for $30, will be able to go on Facebook, although at slower speeds.

However, users won’t be able to click to outside sites unless the pay extra for data. Still, T-Mobile is hoping the lure of free access to the world’s largest social network will attract more customers. Launched last March, GoSmart has since pulled in “hundreds of thousands” of users looking for low-cost, unlimited mobile service, according to T-Mobile.

The plans range from $25 a month to $45 for unlimited talk, text and 5GB of 3G data. So in addition to serving as an initial selling point, the free Facebook access could also lead users to upgrade to the data plan if they want to be able to link out to other sites from the social network.

T-Mobile, which has always been known for offering lower-cost mobile options, earlier this year branded itself as the “uncarrier” for doing away with the contracts and device subsidies that prevail in the U.S. mobile market. But with the other major carriers now pushing more aggressively into the prepaid arena, T-Mobile is looking for new ways to differentiate itself.

How much of a draw the free Facebook service will prove to be in the U.S. isn’t clear, since people can also turn to WiFi networks at home or in public locations to go on the social network. The desktop also remains an option for many in the U.S., which isn’t always the case in developing regions.

But there is little question that Facebook use is shifting from the desktop to mobile. The social network had 874 million active mobile users as of the third quarter, with almost half its 1.15 billion users accessing its Web site from a mobile device. And earlier this year, Nielsen data showed that monthly time spent on Facebook in mobile edged out that on PCs.