(AP) -- T-Mobile USA is doing something unusual for a phone company: enabling free calls on computers between Facebook friends.
T-Mobile released a series of software add-ons for the most popular browsers Tuesday. Once installed, a phone icon appears beside each name in the chat section of the user's Facebook page. Clicking the icon places a call through the Internet connection.
Only the caller needs to have the software installed for the call to go through, but both participants need to be logged in to Facebook and have headsets or microphones and speakers.
The software add-ons are branded "Bobsled by T-Mobile." The company plans to use the brand for other Internet-calling features, such as phone apps that can place calls directly to Facebook friends.
Brad Duea, T-Mobile USA's senior vice president of marketing, says the point of "Bobsled" is to put T-Mobile's brand in front of more people. (That brand may go away in a year or two anyway, as AT&T Inc. seeks regulatory approval to buy T-Mobile for $39 billion.)
T-Mobile could also add advertising or start charging for calls from PCs to phones.
Smaller companies have offered Internet calling with various degrees of integration with Facebook. T-Mobile USA, which doesn't own any conventional phone lines in the U.S., also sold conventional Internet calling devices for a few years. They worked with regular home phones instead of PCs.
For Facebook calling, T-Mobile is using backend technology from Vivox Inc., which provides voice communications for several online games, including "Star Wars Galaxies."
The "Bobsled" software has been available for a few months as T-Mobile and Vivox tried them out under the "Vring" name. The connection to T-Mobile was secret.
Explore further: Motorola and Skype announce certified Bluetooth headset