Facebook (Nasdaq: FB), owner of the world’s most popular social network, is testing voice calls in the U.S. on its Messenger application for Apple Inc.’s iPhone as it seeks to add more mobile services.

The company said in an e-mail that it’s extending a test begun in Canada earlier this month. Callers can use the app to make phone calls to friends over data networks instead of the voice service provided by traditional phone companies.

The news came shortly after Facebook announced a new social media-focused search application called Graph Search as it steps up its competition with Google and other sites such as LinkedIn and Yelp.

“We started testing this in Canada the first week of the year and today we’re extending that test to the U.S.,” Facebook said. “We were able to expand the test so quickly because it went well in Canada and we wanted to expand the audience.”

Facebook, based in Menlo Park, California, is stepping up its efforts in mobile to attract more consumers who use the service via tablets and smartphones. About 60 percent of Facebook’s more than 1 billion members used mobile devices to access the service at the end of the third quarter, up from less than half of them a year earlier, according to a filing.

To make a call on the application, users tap on an “i” and then choose the option for “free call.” The application helps members quickly share messages with friends via mobile devices, including features for scrolling through a list of friends and checking on past notes from users.

Facebook slipped less than 1 percent to $29.85 Wednesday at the close in New York. The shares have fallen 21 percent since the initial public offering price of $38 in May.