Facebook and T-Mobile US are working together to allow the social network to join Binge On, a program that lets T-Mobile customers watch mobile video from partner services without tapping their data plan.

The two companies have been working for some time, sources said, to add Facebook video to the list of services that T-Mobile supports. In exchange for the unlimited video streaming that comes with Binge On, customers agree to view video sent over the cellular network in less-than-HD quality.

Netflix, HBO and ESPN were among the services that were part of Binge On when T-Mobile introduced it last year. It has since added other video services and made it easier for customers to choose not to take part in Binge On. YouTube was added in March, leaving Facebook and Snapchat as two noticeable missing players.

While T-Mobile has been open to including all interested parties in Binge On, it requires some technical work on the part of video services to make sure their video streams are identified to T-Mobile’s system. That work is still ongoing with Facebook, sources said.

The move comes as Facebook is placing increasing emphasis on video, and live video in particular. Allowing T-Mobile’s users to see the video without affecting their data caps could encourage them to watch more video, while not being part of the service could lead customers to watch video from competing services that are part of Binge On.

There could be another benefit for Facebook to joining Binge On: The move might assuage critics in India (and elsewhere) who have opposed the company’s Free Basics program, where Facebook partners with carriers to offer free access to Facebook and certain other sites in emerging markets. The idea of offering some of the Internet — but not all of it — for free has drawn the ire of staunch net neutrality advocates. Offering Facebook video for free might give the company something similar to point to that is actually working in the U.S.

T-Mobile and Facebook are also exploring whether some version of the Free Basics approach makes sense in the U.S., according to a source. Back in March, a few T-Mobile users noticed a bizarre “Free data” message inside the Facebook app, but nothing ever came of it, at least not publicly.

A Facebook spokesperson declined to comment, as did a T-Mobile representative.

Additional reporting by Kurt Wagner.