South Korea's largest mobile operator SK Telecom (Nasdaq: SKM) announced on Tuesday the world's first commercial voice-over-LTE (VoLTE) service. (See SK Launches VoLTE Service.)

To use the 4G voice service, called HD Voice, SK's LTE subscribers will need a Samsung Corp. Galaxy S3 LTE smartphone with embedded 4G voice support, which the operator will start selling on Aug. 8. For existing Galaxy S3 LTE owners, SK says it plans to provide firmware upgrades this month. Other LTE devices will not support the HD Voice service, but SK says it plans to include it as a basic feature in most of its future LTE smartphones.

The 4G service does not require an extra subscription, and it is priced at the same per-second billing rate as the operator's 3G voice service, which is KRW1.8 (US$0.002) per second.

The operator claims the new service has not only better voice quality but also faster connection times compared to 3G voice services. SK says the call connection time for the HD Voice service is less than 0.25 to 2.5 seconds, while 3G voice calls take on average 5 seconds to connect.

According to SK's press release, the operator ensures Quality of Service (QoS) for the IP voice calls by applying a QoS Class Identifier (QCI) in the LTE network so that the HD Voice data traffic is prioritized and handled first.

Beyond the new voice capability, SK says it also plans to offer new "value-added" services. The operator didn't specify what those will be exactly, but mentioned "in-call voice-to-video call switching" and content sharing by adding Rich Communication Suite (RCS) services.

SK, which has about 26 million customers, had 4 million LTE subscribers as of July 20.

Why this matters
SK's HD Voice is the first commercial VoLTE service in the world, let alone the highly competitive South Korean market. And the availability of only one smartphone that can support the offering shows just how early it is for the 4G voice services. SK's rivals KT Corp. and LG Telecom (LG U+) are expected to follow with their own 4G voice offerings this fall, while other operators -- particularly those in the U.S. -- will be watching this service launch closely as they prepare their LTE networks for voice services. (See T-Mobile Hunts for Voice-Over-LTE Talent, Sprint Hiring for 4G Voice and VZ Plans Nationwide VoLTE in 2013 .)

The pricing of the new service may also stir up some controversy in the South Korean market, where mobile operators are allowed to charge extra for or block altogether mobile VoIP services from third-party over-the-top (OTT) providers, thanks to a recent ruling by the Korea Communications Commission. So, in theory, SK now has its own IP-based voice service that it offers for no extra subscription, but it can charge or block similar offers from other providers. (See Korea Leads the Charge on Mobile VoIP.)

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— Michelle Donegan, European Editor, Light Reading Mobile