EE, the UK's biggest mobile operator, has confirmed it will launch a voice-over-LTE (VoLTE) service this summer and says the technology will be made available on "the market's most popular new handsets."

VoLTE allows customers to make voice calls over a service provider's 4G network and is supposed to improve call quality and reduce the time it takes to set up a call.

The technology could also help to boost signal strength inside buildings and in less densely populated communities.

Lacking any of the 900MHz spectrum its competitors use to provide 2G voice services, EE has instead been relying on 1800MHz airwaves, but these above-1GHz frequencies tend not to penetrate walls or cover wide areas as well.

VoLTE would bring into play the 800MHz airwaves EE secured during the UK's 4G spectrum auction in early 2013. The operator has already carried out trials of VoLTE in the 800MHz band in a rural part of Oxfordshire it says was previously unconnected.

In April, as an interim step to VoLTE, EE launched a WiFi calling service that allows voice calls to run over a local WiFi network in preference to the cellular service. (See EE Hopes WiFi Calling Will Hit the Spot and Can WiFi Calling Find Its Voice?)

The drawback is that calls will not hand over from WiFi to cellular, or vice versa, meaning customers may lose the connection if they are moving around during a call.

VoLTE will also allow calls to switch from the 4G network to a 2G or 3G service mid-call -- should a user move outside 4G coverage -- provided the operator has made use of a technology called enhanced single radio voice call continuity (eSRVCC) when introducing VoLTE.

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Vodafone UK , the UK's third-biggest mobile operator, also intends to launch a VoLTE service this summer, as well as a WiFi calling feature, and said it had been testing both technologies in labs for "several months" when announcing its plans in March. (See Vodafone UK to Launch VoLTE in Summer.)

The country's smallest mobile network operator, Three UK , is aiming for a September launch of VoLTE and will also deploy the service in the 800MHz spectrum band, claiming this will allow customers to "make and receive calls in places they've never been able to before." (See 3 UK to Launch VoLTE by September.)

The company, which served 8.4 million customers last year, expects to have 1 million VoLTE users this year and 7.5 million in 2016.

Telefónica UK Ltd. , which trades using the O2 brand, is the only one of the UK's four mobile network operators yet to announce firm plans for VoLTE.

Telefónica has agreed to sell O2 to 3 owner Hutchison Whampoa Ltd. (Hong Kong: 0013; Pink Sheets: HUWHY) for £10.25 billion (US$15.8 billion). A merger with 3 would create the country's biggest mobile operator by customer numbers but has yet to secure the approval of competition authorities. (See Telefónica Seals $15.2B O2 Sale to Hutchison.)

Watchdogs are also scrutinizing a proposed £12.5 billion ($19.3 billion) takeover of EE by UK fixed-line incumbent BT Group plc (NYSE: BT; London: BTA), which currently relies on a wholesale agreement with EE to provide BT-branded mobile services. (See BT Locks Down £12.5B EE Takeover Deal and BT Threatens Price War With New 4G Offer.)

BT decided to spin off its BT Cellnet mobile division back in 2001. The business was subsequently acquired by Telefónica and rebranded as O2.

— Iain Morris, , News Editor, Light Reading