Why No Sprint HD Voice on the iPhone 5?

The won't support Sprint's new high-quality voice calling system, Sprint confirmed to Phone Scoop today. In fact, while the iPhone 5 supports high-quality ("wideband" or "HD") voice calls, it won't do so on any U.S. network, probably ever.

Unfortunately, there's some misinformation out there including an inaccurate report by the generally reliable iMore, so I wanted to clear up why this is happening.

HD Voice uses a different compression method to represent a wider range of frequencies than previous voice calling systems. That lets phones better handle background noise and it lets them better represent all voices, removing the harshness or "computeriness" you hear on a lot of cell phone calls.

There are three ways to do high-quality, or "wideband" voice calls.

One is to use a new codec, called AMR-WB, over a "3G GSM" (UMTS) network. That's what some European carriers are doing and what's in the iPhone. This is relatively easy to implement on the phone side, provided that the network supports it. In the U.S., only AT&T and T-Mobile would be eligible to do this, and they won't because they're focused on 4G (see below.)

The second is to use a different new codec, called EVRC-NW, over a 2G CDMA 1x Advanced network. 1x Advanced is a proprietary Qualcomm extension to older 2G CDMA networks, which greatly increases their capacity, and lets carriers turn some spectrum over to new 4G networks. This is the route Sprint is taking. The iPhone doesn't support it.

The third is as part of a total changeover of voice calling from old 2G networks to new 4G networks, something called VoLTE (voice-over-LTE.) VoLTE is the biggest change in voice calling since digital cell phones; it basically changes all calls into a voice-over-IP-like form and pipes them over the LTE data network. It uses the same codec as the GSM approach, AMR-WB, but in a totally different overall transmission format. This is what Verizon has demoed in the past, and plans to do. The iPhone 5 doesn't support it.

AT&T and T-Mobile will probably also go to HD Voice over VoLTE, because that's the real future; AMR-WB over UMTS is easy from a device perspective, but just increases the burden on those carriers' slammed 3G networks. MetroPCS, , is already going to VoLTE, albeit without any HD voice codecs.

For more, see our explainer at ExtremeTech, "What is HD Voice?"

The Big HD Voice Mess
HD Voice is going to be a big letdown, at least for its early years. There are too many incompatible approaches, and so far none of the carriers involved have said anything about interoperability.

When , company execs said the 3GPP, the industry body in charge of these things, was just starting to hash out how carriers were supposed to talk to each other with HD Voice. But wait! Sprint's 1x Advanced approach isn't covered by the 3GPP talks! And no U.S. carrier has yet said how its HD Voice approach will interoperate with landlines.

The result is going to be extremely limited HD Voice experiences in the U.S. for at least a few years. It'll be restricted to calls between limited sets of phones, probably on the same carrier, and it won't be on the iPhone 5.

For more, see and the slideshow above.