MetroPCS today became the world's first operator to go live with commercially available Rich Communications Services on an LTE network.

"We believe RCS is a tremendous differentiator among prepaid and postpaid competitors alike and recognize that achieving interoperability across U.S. 4G LTE networks is the next key step to paving the way for more innovative services and capabilities in the future," MetroPCS CEO Roger Linquist said in a statement.

The service is based on the GSMA RCS 5.0 standard and is being marketed under the GSMA joyn brand.

Joyn sports IM-like features such as the availability status of contacts, composing indications and group chat. It also allows users to share video, images and files while on messaging or during a call. It also allows users to place voice and video calls over Wi-Fi.

It is being offered as an app on Google Play and the MetroPCS app store, @metro App Store.

Joyn is so far only available for download on the Samsung Galaxy Attain 4G. Additional RCS smartphones will hit shelves later this year and in 2013, and MetroPCS plans to preload the app on smartphones "at a later date."

Although RCS has often been cited as a potential source of additional revenue for wireless providers, MetroPCS is not charging extra for its joyn service. Instead, it is included with the operator's existing LTE plans.

RCS emulates over-the-top services like Skype and Facetime, but offers the interoperability that the third-party apps lack. Interoperability is expected to be the key differentiator between RCS and existing video call and messaging apps.