T-Mobile USA has rolled out voice over LTE in its home base of Seattle, offering high-definition voice and promising benefits to subscribers from a technology that in time could save carriers a lot of money.
VoLTE carries voice calls over a phone's LTE data connection instead of a 3G circuit-switched network. That may eventually mean carriers can operate just one network, but it could also allow them to offer a broader range of services, including video calling. With VoIP, video chat and other communications services readily available "over the top" from Internet companies, carriers want to get into the game with integrated offerings, called rich communications services.
In the Seattle area, VoLTE is now available for the LG G Flex, Samsung Galaxy Note 3 and Samsung Galaxy Light phones. T-Mobile subscribers with those phones can start using VoLTE by getting an update to the latest software. For VoLTE to work, both phones on the call need to have the software.
T-Mobile says VoLTE calls will start faster, with call setup nearly twice as fast as on the traditional circuit-switched connections. VoLTE will also come with HD voice, a technology for better-sounding calls, though T-Mobile already offers a form of HD voice nationwide without VoLTE.
The Seattle announcement on Thursday beat by one day AT&T's planned introduction of VoLTE with HD Voice in four Midwest states. Verizon said Wednesday it would launch VoLTE with both HD voice and video calling later this year. Sprint, which already offers HD voice over its 3G network, has not announced a timeline for VoLTE. MetroPCS, which T-Mobile acquired earlier this year, introduced VoLTE in 2012.
Carriers have been talking about VoLTE for years, but deployment has been slow. One of the hard things about making it work is shifting calls to another type of network when a user leaves the LTE coverage area. To solve that problem, T-Mobile is using eSRVCC (Enhanced Single Radio Voice Call Continuity), a feature from the LTE Advanced set of standards, CTO Neville Ray wrote in a blog post. The new feature will ensure calls don't get dropped when users move into areas that don't have LTE, he said.
T-Mobile said it's now working on launching VoLTE in more cities and on more devices, plus more rich communications services.