One of the new iPhone 5 hardware features announced yesterday was support for wideband audio — or HD voice — which increases the fidelity of voice calls. In the US, the only carrier that has publicly announced support for the HD voice protocol is Sprint, but Phonescoop has learned that the iPhone 5 won't work over Sprint's version of HD voice. As for the technical details, Sprint's HD Voice protocol runs over its 1x CDMA network, whereas the iPhone 5's HD Voice support uses GSM-based WCDMA technology.
WIthout support for Sprint and no current support for wideband audio from Verizon or AT&T (though Verizon tested it last year, and had hoped to launch it at some point in 2012), it seems that no US carriers will be able to use the iPhone 5's new HD voice support when it launches. Given that Apple only announced 20 carriers supporting HD voice (out of the 240 total that will sell the iPhone 5), the odds weren't in the US carrier's favor — but it's still unusual to see a headlining iPhone feature unavailable for stateside users. We've reached out to Sprint to get more details and will update if we hear anything.