U.K.-based BT has done a lot of talking about performing HD voice transcoding for fun and profit, but Deutsche Telekom (DT) is the first carrier actually doing it for customers. In their case, in Germany across its broadband and 3G wireless networks.   Transcoding started on October 9, 2014, according to a DT spokesperson.

HD voice calls are translated in both directions between the G.722 broadband codec and the AMR-WB wireless codec.  G.722 is used as the HD voice codec for DT's broadband voice service and is incorporated into the CAT-iq 2.0 DECT cordless phone standard supported by DT, as well as on an iPhone SIP client for in-home Wi-Fi use.  AMR-WB is used in both 3G networks and in 4G LTE networks as a part of Voice over LTE.

Currently, DT supports HD voice on its 3G network and hasn't announced a date on when it will deploy VoLTE on its LTE network.  The company has been running AMR-WB on its 3G network since November 2011 and started supporting G.722 on its broadband network in January 2012.

Transcoding takes place if both callers are on DT's networks. There is no charge to customers for transcoding in-network.   DT has said it believes there's money to be made for HD voice transcoding between networks, but has not announced if carriers have contracted for the service.

G.722 holds particular significance for a number of reasons.  It is the oldest HD voice codec. First developed for ISDN digital calls, it is incorporated as a standard feature into IP desktop phones, any number of cloud business voice services, the Ooma over-the-top (OTT) consumer and SMB broadband voice service, various Unified Communications (UC) soft clients, and the previously mentioned CAT-iq 2.0 DECT cordless phone standard.  CAT-iq is supported by DT, Orange, and the CableLabs cable technology consortium.

Most recently, Microsoft declared its support for G.722 being rolled into WebRTC.  Transcoding between G.722 and AMR-WB provides an HD voice "bridge" between the wireless and broadband worlds, meaning DT can support a seamless HD voice experience for businesses between existing and established broadband-based HD voice services and wireless services.

DT hasn't addressed the other "elephant" in the room: Network-to-network HD voice interoperability.  Orange made some limited announcements for connecting HD voice calls between its different subsidiaries in 2012 and offering the ability to move HD voice calls between different carrier networks in both AMR-WB and G.722 formats (i.e., wireless and broadband supported).   DT and a number of other Tier 1 carriers have been trying to drum up support for serving as high-level network exchange points to seamlessly move HD voice calls between different carriers, but none of the Tier 1s have announced they are "peering" HD voice calls among themselves.

One party that may be annoyed with DT's announcement is GSMA.  The association recently released a white paper suggesting WebRTC incorporate AMR-WB as one of its mandatory voice standards to avoid the potential headaches of HD voice transcoding, including loss of voice quality and the potential to introduce significant delays between AMR-WB and WebRTC's Opus voice codec.  If DT is transcoding between G.722 and AMR-WB on its own network, it's not unreasonable to think transcoding between AMR-WB and Opus is not as bad as portrayed.