Does AT&T / Sprint / Verizon support iPhone 5 wideband / HD audio?
Wideband audio was announced at Apple's iPhone 5 media event, and 20 carriers are expected to support the technology at launch. Unfortunately for US customers, the major carriers AT&T, Sprint and Verizon are not included in this list.
Apple is working to bring wideband (HD) audio support to more carriers across the globe. Wideband audio provides superior audio quality over current narrowband technology. With narrowband, the midrange frequencies are emphasized, leading to shallow sound. Wideband audio fills out the audio spectrum to provide more natural sounding voice communications.