Sprint is planning to launch HD voice in the next month or two on a market-by-market basis, after working out some initial kinks, a spokeswoman has confirmed to Light Reading.

The carrier first announced support for HD voice last year on the HTC Evo LTE, but it's just now getting ready to bake in network support in select markets.

This time last year, Sprint VP of Product Development Fared Adib said the carrier would fully support the technology as it upgraded its network by the first quarter of 2013. The carrier reports Q1 earnings tomorrow morning, however, and a spokeswoman admits HD voice has taken longer than anticipated.

"We had a few things that came out of our FIT [field integration testing] testing in Q4 that we needed to resolve to ensure a really good customer experience," the spokeswoman writes in an email to Light Reading. "Those have been resolved and now we’re planning the roll-out."

Supporting HD voice is no small task. The wideband codec technology requires both handsets to support it with two microphones and noise-cancelling software, the network to support it and operators to use the same radio standards to hear the full benefit of the improved audio.

The Sprint spokeswoman says that Sprint's HD voice will be limited at launch. Not only can a Sprint customer with an HD voice handset not call another capable phone on AT&T or Verizon, but he can't even call across Sprint's OEMs, Alcatel-Lucent, Ericsson and Samsung. That means that a customer in California on an Ericsson base station can't call one in NYC on Samsung. She said it may take several months to achieve interoperability.

Voice-over-LTE (VoLTE) and LTE-Advanced are also on Sprint's roadmap, according to the spokeswoman, but it has yet to announce timing or any actual deployments.

Sprint competitor AT&T has said it plans to launch VoLTE-capable handsets this year, and SVP Kris Rinne said that HD voice would be part of that strategy. T-Mobile's new iPhone 5 also supports the high-def technology. Verizon Wireless has committed to VoLTE smartphones in2014 but has yet to make a firm commitment to HD voice as part of its 4G-voice strategy.

-- Sarah Reedy, Senior Editor, Light Reading