Building on its launch of Rich Communications Services (RCS)-powered messaging in July, T-Mobile has now added video calling to the mix.

Video calls over T-Mobile US Inc. 's LTE network will work directly from the phone's native dialer via an icon next to the voice call button. It will only show up next to contacts with devices that can support video calling, which at launch includes four Samsung Corp. smartphones. T-Mobile CTO Neville Ray writes in a blog post that the carrier will support seven devices by the end of the year. Apple Inc. (Nasdaq: AAPL) may reveal whether it will support it in the next iPhone at its launch event on Wednesday.

Notably, T-Mobile video calling will include handoff between WiFi and LTE. Ray says that if a video call moves off of LTE or WiFi to a slower connection, the video will seamlessly switch over to a voice call with the option to click back to video when high-speed connectivity is restored. The video calls will count against a user's data bucket.

Ray says that T-Mobile is working with others to eventually support video calling across networks. Verizon Wireless also offers native video calling, but -- as with voice-over LTE (VoLTE) -- the services won't interoperate until the carriers work out interoperability deals. (See Verizon to Launch HD VoLTE in 'Coming Weeks'.)

Figure 1: Video Calling in Action T-Mobile's video calling works directly from the dialer and
supports handoff between WiFi and LTE.

T-Mobile was the first carrier to support RCS in the form of IP text messages direct from the native dialer. (Sprint Corp. (NYSE: S) offers an RCS-compatible mobile app.) And it's making good on its promise to keep adding RCS-powered services its arsenal. These over-the-top (OTT)-like services will get more valuable as more carriers and handsets support them. (See T-Mobile Launches RCS Messaging and Sprint Jibes With OTT Comms.)

For more on RCS, visit the dedicated VoLTE/rich communications section
right here on Light Reading.

T-Mobile's RCS is powered by Mavenir, which was recently acquired by unified communications provider Mitel Networks Corp. Rich McBee, Mitel's CEO, recently told Light Reading that he expects other carriers to launch RCS in the next year as they complete their VoLTE network deployments. Both technologies are enabled by the New IP and an IMS core. (See Mavenir, T-Mobile Confirm US RCS Launches and Mitel to Acquire Mavenir for $560M.)

"The reality is RCS is the way the carriers can maintain relevance in their space, because [OTTs] will use their pipes anyway," McBee says, adding, "The IP network will give them the ability to get in and out of things that work and test things and create relevancy for them in a market with a lot of competition."

— Sarah Thomas, , Editorial Operations Director, Light Reading