As a part of all 4G LTE rate plans, and enabled smartphones, joyn by MetroPCS will provide customers the ability to share contact information and status, content, as well as participated in “enhanced” chat which allows for group messaging and provides notifications of read messages. The standard also allows for Wi-Fi and video calling, which may be a handy alternative to FaceTime.
Much like Google Talk, this feature will allow your contacts to see your status if you are available to chat or not. The service will allow for location sharing as well, and the exchange of content while on a call or during a chat.
The goal is to allows these features be shared by customers no matter what device or OS they are using, but for now, joyn is available only on the Samsung Attain 4G. Of course, MetroPCS will be offering additional RCS compatible devices through the rest of this year and 2013.
sources: MetroPCS via The Verge