Yes, the shiny new Apple iPhone (News - Alert) 5 does indeed support HD voice ("cellular wideband audio" as Apple has dubbed it). "Over 20 carriers" will support HD voice at product launch, according to Apple (News - Alert).
It's a feature overseas carriers have been waiting for, but some questions remain as to the details on what networks HD voice will be supported – CDMA, HSPA+ and/or LTE.
The iPhone 5 certainly has the handset hardware to support a kicking HD voice (and music playback, for that matter) experience. New audio features on the phone include a beam-forming directional microphone system for higher quality sound.
There are three (3) microphones built into the iPhone 5 – a feature/trick that you've only previously seen on higher-end room-sized conference speaker phones from folks like Polycom (News - Alert).
The iPhone 4 and 4S, as well as many higher-end Android smartphones, have two (2) microphones to help with echo cancellation and background noise filtering; adding a third mic for better sound processing goes under the "Brilliant (News - Alert) idea – why didn't I think of it?" category.
Speaking of sound processing, I'm going to assume Apple rolled in Audience's earSmart sound processing algorithms directly onto the A6 chip. Apple had incorporated an Audience (News - Alert) earSmart chip into the iPhone 4 and then licensed and integrated the earSmart technology onto its A5 chip with the release of the iPhone 4 S.
Putting the technology directly onto the phone CPU cuts down on part count (cheaper) and helps save power (less energy, powering multiple parts).
Apple now supports LTE, so it should be a given that Voice over LTE (VoLTE) and AMR-WB is supported. And if you're supporting the AMR-WB wideband codec, you can support HD voice on 2G GSM and 3G HSPA networks around the globe that already have HD voice service turned on.
Does Apple support Qualcomm's 3G CDMA EVRC-NW codec (Well, does Apple support 3G CDMA)? We'll have to wait to get more details on Sprint's iPhone 5 configuration when sales start, but I wouldn't be surprised at either "yes" or "no" at this point.
About the only truly unanswered question is if Apple will support HD voice on older model iPhones through the iOS 6 release, specifically GSM/HSPA+ network iPhone 4 and 4 S models. Both earlier models have the embedded hardware to support HD voice, as noted above.
I suspect both Apple and mobile carriers will keep HD voice an iPhone 5 "exclusive" feature to tempt/push users to upgrade to the latest and greatest hardware – and locking them into a new contract term.