T-Mobile has lit up Voice over LTE (VoLTE) in Seattle, allowing those with certain smartphones to make voice calls routed over 4G and with the benefit of better quality. Currently supported on the LG G Flex, Samsung Galaxy Note 3, and Galaxy Light, T-Mobile's VoLTE follows AT&T's launch of its equivalent service earlier this month, though only on a single phone.
Meanwhile, Verizon has announced that it will be turning on VoLTE later in the year.
It's not just HD Voice that T-Mobile's VoLTE will include - which, in fact, the network has been offering on select devices for more than a year - but faster call setup times. It'll also stop the phone from switching to HSPA+ at best when on a voice call, which means data services on the device will continue at LTE rates.
Step outside of an LTE area, meanwhile, and the call should automatically switch from VoLTE to a traditional call across HSPA+ or even 2G service, T-Mobile promises.
As for when it will extend beyond Seattle, T-Mobile doesn't have a set roadmap it's sharing yet, but says that both service and supported devices will come in time. Those with compatible devices will need to update their firmware in order to use VoLTE.