AT&T lays claim to being first domestic operator to support international VoLTE roaming services, though U.S. support remains spotty.
AT&T expanded voice-over-LTE roaming into Japan, signing a deal with NTT DoCoMo to support AT&T’s high-definition voice service for customers traveling in the Asian country.
AT&T said the roaming service allows customers to call other AT&T Mobility customers with compatible devices and when in a VoLTE coverage area. Those customers will also be able to simultaneously conduct a voice call and access internet services while on NTT DoCoMo’s LTE network.
Both carriers initiated their respective data-based voice services in mid-2014, which analysts at the time said could allow carriers to achieve up to 40% more spectral efficiency running voice traffic over their LTE networks compared with legacy systems. Both carriers also have some history together as DoCoMo owned a 16% stake in AT&T Wireless Services in early 2001, before selling off that stake as part of Cingular Wireless’ acquisition of AWS in 2004.
AT&T claims it’s the first U.S. carrier to offer VoLTE roaming in Japan, having apparently beat rival Verizon Communications for the honor. Verizon last summer announced plans to allow customers from Japanese operator KDDI to access VoLTE services while roaming on its U.S. network, with plans for Verizon Wireless customers to gain similar access when traveling to Japan by the end of 2016. However, Verizon has so far not announced the roaming capability.
Domestic VoLTE roaming is still somewhat limited, with Verizon Wireless, AT&T Mobility and T-Mobile US all in varying stages of working through network support.
AT&T Mobility and Verizon Wireless said they began supporting limited cross-carrier VoLTE roaming in late 2015, having initially announced work on those efforts in late 2014. Those efforts have reportedly progressed to allow for cross-carrier support, but accessibility is still somewhat limited.
T-Mobile US has said it was also working with AT&T Mobility and Verizon Wireless on VoLTE interoperability and that most of its voice traffic runs over its internal VoLTE platform. However, the service is still not officially set up for cross-carrier support.
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