T-Mobile wins the prize this week for most innovative U.S. cellular carrier. The self-styled "Un-Carrier" announced on May 22 that it is launching Voice over LTE (VoLTE) in Seattle on three different devices. CTO Neville Ray and the company's PR team also get big points for actually explaining how VoLTE is better and what eSRVCC is.
Devices supporting VoLTE via over-the-air software upgrade include the LG G Flex, Samsung Galaxy Note 3 and Galaxy Light – two more than in AT&T's rollout announcement. T-Mobile is clearly supporting some existing customer devices, while AT&T has said nothing about what or if any deployed devices will be supported.
More devices and more cities are expected in the months to come, but there's no indication as to when or where rollouts will occur. T-Mobile tends to do first, then announce, so this is no surprise to anyone other than their competitors.
Ray does muddy the water a bit in a couple of areas. Subsidiary MetroPCS was indeed the first to launch VoLTE in the U.S. in 2012, but it did not support HD Voice at time of launch. He also says the company has supported nationwide HD voice since January 2013 "something our competitors couldn't do without VoLTE." Sprint is supporting HD voice on its legacy 3G CDMA network with a different encoding scheme (codec) called EVRC-NW, so it doesn't need VoLTE. AT&T could support HD voice on its HSPA+ network with a software upgrade – just like T-Mobile did in late 2012 – but it claims RF bandwidth issues prevent it from doing so.
Balancing off the MetroPCS and "You need VoLTE" assertions is Ray's short explanation of how VoLTE calls are carried on T-Mobile's "wickedly fast" LTE network and the "tricky bit" is keeping smooth mobility between the various radio layers.
Enhanced Single Radio Voice Call Continuity (eSRVCC) is billed as a "new" LTE Advanced function with T-Mobile claiming it is the first to deploy it in the U.S. The technology prevents calls from being dropped if a caller moves from an LTE service area into a HSPA+ or 2G coverage area.
Yesterday, I predicted T-Mobile would announce VoLTE at a time and a place of its choosing, likely beating Sprint to the punch. I almost wrote that I expected T-Mobile to beat Verizon to deployment, but decided not to place that bet. Like most U.S. carriers, I should stop learning to bet against the Un-carrier.
T-Mobile's launch puts Verizon in an embarrassing position, since both it and AT&T have now introduced VoLTE into service while Verizon yesterday had a vague statement of a VoLTE launch sometime in 2014. Verizon has spent the past 24 hours trying to flood Twitter with pointers to its "announcement."
Edited by
Alisen Downey 
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