T-Mobile has expanded its "Music Freedom" program to include Google Play, Xbox Music and 12 other services. (Photo by: Matthew Williams/Bloomberg)

T-Mobile announced Monday that it is expanding its program to give users free access to streaming music to 14 additional services. The program, which already gives T-Mobile subscribers the option to listen to services such as Pandora, iTunes Radio and Spotify without racking up data costs, now includes access to Google Play, Xbox Music and a variety of small services.

The program was first introduced in June and has been very successful for the mobile carrier, said Matt Staneff, T-Mobile's vice president of marketing. Customers, he said, have logged a 300 percent increase in the amount of music they listen to since the feature went live. The company has also conducted research, he said, that's shown one in four U.S. consumers view the music perk as a reason to switch to T-Mobile.

T-Mobile has been asking users to submit their suggestions for streaming sites that should be added to the list of services that don't incur data charges on the network. Google Play, Staneff said, was one of the top suggestions. He also added that any music service can ask to be a part of the program. Smaller additions on Monday included Saavn, a station that only plays Indian music, particularly Bollywood tunes. Another, Digitally Imported, is all-electronic dance music, all the time.

The program has been popular with users, but has drawn some questions from net neutrality scholars, who wonder about how exactly T-Mobile is paying for the 66 million songs it offers every day -- roughly 200 terabytes of data, Staneff said. As my Post colleague Nancy Scola reported, the net neutrality rules recently suggested by President Barack Obama would prohibit internet service providers from charging companies for special access to their customers. That could be strictly  interpreted to include apps in which a content company -- i.e. a music service -- covers users' data costs.

But T-Mobile was clear in its statement Monday that the music services themselves aren't paying for access to the program -- though it didn't disclose who is. Per the press release: "not only is Music Freedom available for T-Mobile customers at no extra charge, it’s also completely free for music streaming providers. No backroom deals. No paid prioritization. Just you and your music − unleashed."

Staneff said that T-Mobile has definite plans to expand the Music Freedom program to other services in the future, though he didn't have any specific details on what 's coming next and when.