EE announced today that it is rolling out a new service this autumn that will allow some of its customers to make mobile phone calls over a Wi-Fi connection.

The service, known as voice over Wi-Fi (VoWi-Fi), will enable EE customers to call other phones when there is no cellular signal present, providing they have a compatible handset and access to a reliable Wi-Fi connection. 

One of the reasons EE is introducing VoWi-Fi is to ensure people can still make calls in buildings, which can’t always be penetrated by mobile networks.

Speaking at EE’s network testing facility in Borehamwood, North London, EE’s director of network services and devices, Tom Bennett, said: “There are places where we don’t currently penetrate. I’m not going to hide that.

"I run the best network and I put a lot of work in. But equally I can’t cover everywhere.”

One particular area where EE’s customers get poor coverage is London's Canary Wharf, which is home to the UK headquarters of some of the world's biggest banks, including HSBC and JP Morgan, and hundreds of thousands of office workers between Monday and Friday.

One way of improving mobile coverage in buildings is to send mobile signals out on lower frequencies. 

However, Howard Jones, a member of EE’s media relations team, said this isn't always enough. “It doesn’t matter what spectrum or how low the frequency is, building regulations mean that Canary Wharf and new trains are almost impenetrable.”

When the user has access to both mobile networks and Wi-Fi, the VoWi-Fi technology will automatically connect to whichever one offers the best connection.

EE was unable to say how many of its customers will be able to use VoWi-Fi when it is launched. This is largely because VoWi-Fi requires new telecoms technology to be built into handsets.

“It’s basically for new phones and we’re working on some of the existing phones in the EE range that are upgradable,” said Jones, adding that certain devices will be compatible after they receive a firmware update. 

EE said it is currently in talks with a number of large handset manufacturers in order to ensure that they put the necessary technology into their next generation of devices.

The company acknowledged that it's already possible to call other phones over Wi-Fi using voice over IP (VoIP) technology, which is built into apps like Skype. 

However, EE pointed out that VoWi-Fi will be built into a phone’s native dialler, whereas VoIP services typically require the user to open an app like Skype before they can be used. EE also claimed VoW-Fi will offer higher quality and a greater degree of reliability than VoIP services. 

Ahead of the rollout, the VoW-Fi service is being trialled by 500 EE staff.

VoWi-Fi is being rolled out as part of a £275 million investment EE is making into improving the quality of voice calls made over its network, which falls under the £1.5 billion investment EE is making across its network as a whole. 

The £275 million has already been used to upgrade more than 6,000 2G sites and increase capacity on 2,000 3G sites, in order to support over 900 million calls being on the EE network made every week.