Verizon and KDDI Corporation announced today the companies have signed a Voice over LTE (VoLTE) roaming agreement, which will initially allow KDDI customers to get high-quality voice services while traveling in the U.S. when they roam on Verizon’s 4G network, the largest 4G LTE network in the country.

Verizon is the first U.S. wireless company to offer foreign travelers VoLTE service while in the U.S. KDDI customers who visit the U.S. will have superior quality communications with family and friends, simply by using their VoLTE-roaming compatible phones.

Takashi Tanaka, president of KDDI, said, “I am immensely proud of becoming Verizon’s first VoLTE roaming partner. Through this successful VoLTE roaming launch, KDDI will deliver a superior experience to our subscribers while they are in the United States, the country that Japanese visit more than any other. I look forward to providing Verizon’s subscribers the same experience in Japan in the very near future.”

KDDI customers will begin roaming on Verizon’s 4G LTE network in June when KDDI’s new VoLTE roaming-compatible smartphone model will be on market.

“We’re confident that we can provide KDDI customers with seamless service on the most reliable 4G LTE network available in the U.S.,” said David Small, executive vice president of wireless operations at Verizon. “Later this year, Verizon customers traveling to Japan should expect to get a great VoLTE wireless experience as well.”

Verizon has been testing VoLTE roaming with multiple carriers and expects to offer its customers the ability to use its VoLTE service, HD Voice, while traveling in Japan later this year.