Cell tower (Flickr user forklift)

Deutsche Telekom-owned T-Mobile USA, the nation’s fourth largest wireless carrier, on Thursday announced it’s started gradual deployment of Voice Over LTE (VoLTE) technology, starting with Seattle.

The move comes just as rival AT&T last Friday brought both VoLTE and HD Voice technologies to select markets and as Verizon Wireless pledged to roll out VoLTE later this year.

That major U.S. telcos are racing to have VoLTE ready at this particular moment in time may have something to do with Apple’s expected launch of the iPhone 6 this Fall, alongside iOS 8 which is said to support making voice calls over high-speed LTE networks out of the box…

According to T-Mobile, VoLTE is available in the Seattle area for T-Mobile’s existing subscribers who own an LG G Flex, Samsung Galaxy Note 3 or Galaxy Light devices.

“Our friends at MetroPCS were the first to launch VoLTE in the U.S. back in 2012, and we’ve been working hard on a LTE Advanced version of VoLTE, which we plan to roll out to more T-Mobile customers throughout the coming year,” noted Neville Ray, Chief Technology Officer with the carrier.

Additional VoLTE cities and devices will be announced in due time.

Voice over LTE, as the name implies, brings both data and your voice onto the same radio layer.

Current implementation separates the two – that’s why you can’t make voice calls and surf the web simultaneously on your smartphone.

Neville shares the nitty-gritty:

VoLTE calls will be carried over IP on our LTE network instead of a circuit-switched path on our 4G HSPA+ network. This is advantageous because your phone stays on our wicked fast LTE network to make a call.

The tricky bit in all this is the smooth mobility between our various radio layers. Enhanced Single Radio Voice Call Continuity (eSRVCC) is a new LTE Advanced function and we’re excited to be the first to deploy it in the U.S.

All of this basically helps ensure that your capable phone won’t drop a call if you leave an LTE area and it switches to 4G HSPA+ or 2G coverage.

Again, because both voice and data are on the same radio layer, you’ll be able to surf the web at 4G LTE speeds while on a call. Besides, VoLTE call setup times are “almost twice as fast” as a non-VoLTE call setup, noted the carrier.

T-Mobile has been offering HD Voice since January so this technology is also included with VoLTE. Also known as Wideband Audio, HD Voice basically taps the extended frequency range for crystal clear conversations.

All iPhones since the iPhone 5 support HD Voice.