AT&T says its VoLTE customers can roam on DoCoMo in Japan

AT&T’s LTE customers can now make voice-over-LTE (VoLTE) calls when they are travelling in Japan – but only to other 4G LTE-equipped customers of AT&T.

AT&T and Japan’s NTT DoCoMo announced this week that they are launching VoLTE roaming in Japan.

“Customers will be able to enjoy the benefits of VoLTE when roaming in Japan as they do at home,” said Bill Hague, AT&T’s executive vice president global connection management. “It’s another example of our constant work to improve the experience for our customers both at home and abroad.”

The deal does not appear to be two-way: NTT DoCoMo has not said that its customers can use VoLTE when roaming on to the AT&T network in the US.

AT&T said it is the first US telecommunications company to offer VoLTE roaming to customers traveling in Japan.

KDDI announced in June 2016 that its customers would be able to use VoLTE roaming via Verizon Wireless when travelling in the US. David Small, executive vice president of wireless operations at Verizon, promised at the time that Verizon customers would be able to roam with VoLTE in Japan “later this year [2016]” but the company has made no follow-up announcement.

Japanese operators appear to be in the lead with what seems to be an enormously tricky challenge of getting VoLTE calls to roam. DoCoMo announced in 2015 that it would allow international roaming in South Korea, via KT – several months after trials with both KT and Verizon of the US. DoCoMo also tried out VoLTE roaming with Hutchison’s 3 Hong Kong at the start of 2016.

More than 300 million people in the US live within LTE service areas. VoLTE uses LTE’s IP capabilities to transmit voice, while older 4G phones revert to circuit-switched 3G for voice calls. Suitable 4G phones can also transmit voice at high-definition quality.