The iPhone 8 and the iPhone 8 Plus include support for the Enhanced Voice Services (EVS) audio codec that offers improved voice quality and better call reliability, KDDI president Takashi Tanaka told Engadget Japan in a recent interview.
EVS is the first codec that offers up to 20 kHz audio bandwidth for higher quality audio, higher frame/packet error resilience, and higher compression efficiency than other speech codecs for a better user experience.
In the United States, T-Mobile supports Enhanced Voice Services and has offered EVS since early 2016. According to T-Mobile, EVS on its network offers improved voice call reliability in areas of weaker signal for fewer dropped calls and higher-fidelity calls for more realistic voice audio.
AT&T, Sprint, and Verizon have not yet announced support for EVS.
Apple does not mention support for the feature in its iPhone 8 documentation, but UK carrier EE also recently confirmed that the iPhone 8 and 8 Plus work with EVS in a press release announcing EVS support on its network.
Along with T-Mobile and EE, several other carriers in Europe and Asia also support EVS, including Vodafone Germany and NTT DoCoMo.