One of the new features in Apple’s (AAPL) iPhone 5 is wideband audio, more commonly known as HD voice. The technology dramatically improves call quality by extending the frequency range of audio signals transmitted over cellular networks. Sprint (S), thus far, is the only carrier in the U.S. who supports the service, however the company has confirmed to Phone Scoop that the iPhone 5 won’t work with its HD voice technology. While the majority of carriers that support the protocol do so on a WCDMA network, Sprint’s HD voice service is operated over CDMA 1X Advanced technology. Apple claimed that 20 carriers around the world would initially support the feature, but unfortunately it is now clear that none of those carriers are located in the U.S.