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May 20, 2014

HD voice USA: An Inventory of Mobile Carriers

If you think HD voice will simply "work" on your current mobile phone all the time once you buy a new AT&T, Sprint, or T-Mobile US phone, think again. Despite the hype, there are a lot of holes to fill in the bigger picture.  Legacy networks and handsets, new VoLTE (Voice over LTE) turn ups, and incompatible encoding types are going to cause a lot of frustration for consumers in the months ahead.

The first thing to wrap your head around is each of the four largest cellular carriers in the U.S.—AT&T, Verizon, Sprint, and T-Mobile US –are operating and deploying two different networks:  A 3G or "legacy" network and a 4G LTE network. 

Ultimately, everyone will be HD voice when everyone is running VoLTE.  That won't be for a large number of months, perhaps years.

Two of the four, Sprint and T-Mobile US, support HD voice on their legacy networks.  Sprint is supporting HD voice on its 3D CDMA network using Qualcomm's 1X Advanced technologies.  It is the only carrier in the U.S. and  appears to be one of the few in the world supporting HD voice on CDMA; everyone else is going VoLTE. 

T-Mobile spun up nationwide HD voice coverage over a year ago on its existing HSPA network via software upgrade, so kudos to them.   Via Twitter, CEO John Legere claimed it is the carrier moving the most HD voice, but hasn't provided statistics or other details.  Certainly, Legere's claim is correct for the U.S. marketplace, since Sprint won't have nationwide coverage until sometime later this year—If their estimates are to be believed.

Both Sprint and T-Mobile are in the process of turning up LTE networks.  Neither carrier has said when they will turn up VoLTE.  At one point, Sprint insiders suggested 2015.  T-Mobile will deploy VoLTE at a time and place of its choosing and probably before Sprint.

AT&T and Verizon will only support HD voice via VoLTE moving forward.  AT&T has chosen not to support HD voice on its 3G network, citing RF bandwidth considerations.  Verizon, while not commenting publicly, probably did not want to invest the time and money to support a high end feature on their existing 3G CDMA network.  Given Verizon's difficulties in getting VoLTE out the door, this appears to be a good move both from an engineering and cost standpoint.

The two keys for carriers to exchange HD voice calls from end-to-end are at the codec (encoding) level and network connectivity level.   Network connectivity is the easier of the two.  AT&T has been testing a SIP peering architecture for a couple of years, so presumably it should be able to exchanges HD calls with other Tier 1 carriers in short order. 

However, carriers have not detailed any plans for exchanging HD voice calls. There's no timetable, so it could be 2015, or later, before U.S. VoLTE networks are capable of delivering end-to-end HD service outside of their own network boundary.  




Edited by Maurice Nagle


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