iPhone 5 is incompatible with HD Voice by Sprint
With its three microphones and support for wideband audio, also marketed as HD Voice by some wireless carriers, the iPhone 5 is the best calling device ever made by Apple. Yet the improvement of in-call audio quality does not depend solely on the device as the carrier needs to support the necessary codecs on its network.
Now, Sprint has been promoting HD Voice service ever since the HTC EVO 4G LTE hit the shelves, which might lead one to believe that the iPhone 5 will also take advantage of the new standard when running on the carrier's network. However, it won't, as Sprint spokesperson Michelle Leff Mermelstein confirmed for Phone Scoop. The reason for that is compatibility: while wideband audio operates on WCDMA networks, the version of HD Voice offered by Sprint works over CDMA 1x Advanced technology.
So even though there will be 20 wireless carriers around the world that will offer HD Voice on the iPhone 5 at launch, Sprint will not be one of them. In case you are wondering what you'll be missing, check out this impressive HD Voice demo comparing the new standard versus the mediocre in-call audio quality we are all accustomed to.
source: Phone Scoop