For wireless customers in the US, the road to Voice over LTE (VoLTE) has been long and filled with false promises from carriers, but it's finally here. T-Mobile has flipped on VoLTE in Seattle, with plans to expand the rollout through 2014 and beyond. But at least at the start, it's slow going. VoLTE is only available on three T-Mobile devices right now: LG's G Flex, the Samsung Galaxy Note 3, and the Samsung Galaxy Light — a phone most people have never even heard of. CTO Neville Ray announced the milestone in a blog post today while highlighting some of the benefits that come with VoLTE. Those include including faster call connection times and, in Ray's own words, "the ability to enjoy lightning fast LTE data speeds while on a call."

HD Voice is another perk typically associated with VoLTE, but T-Mobile is quick to point out that it's been offering the higher-quality voice feature across the US for some time now. Just what is VoLTE? GSM and CDMA networks use old-fashioned circuit switching to handle voice calls, but VoLTE takes a more efficient approach by turning your conversations into another type of data that's transmitted via a carrier's IP technology.

AT&T is set to launch its own VoLTE-powered HD Voice service beginning tomorrow, trailing T-Mobile by only a day. But to its credit, AT&T is launching in more markets: HD Voice will be available in areas of Illinois, Indiana, Minnesota, and Wisconsin. Unfortunately, device selection is even more limited. If you want to use HD Voice with AT&T on day one, you're stuck with the Samsung Galaxy S4 Mini. Like T-Mobile, the company aims to expand availability to new markets as the year progresses.

As for Verizon Wireless, the largest US carrier is still sticking to an unspecific "this year" timeframe. On a call with media earlier this week, Verizon executives revealed that they'll have numerous phones ready for VoLTE when it's eventually turned on. And unlike its rivals, Verizon is going big out of the gate and promising a nationwide launch. HD Voice and a Facetime-like video calling service were the two main points that Verizon highlighted during the call. Both will be easily accessible in the native dialer of compatible smartphones, the executives said. Verizon is also promising to update existing devices already on the market to support VoLTE so long as they contain the required technology. Smaller carrier MetroPCS beat everyone to the punch when it debuted VoLTE in 2012.