Three, the smallest mobile network operator in the UK, is to launch an app that will allow customers to talk and text using a WiFi connection and so improve its indoor coverage.

Dubbed Three inTouch, the app will be available free to all customers from early August, although usage will be deducted from monthly or pre-paid allowances.

Three says the service is “seamless” and customers can simply use their regular mobile phone number.

EE, the largest mobile operator in the UK, also has plans for a VoWiFi launch in the autumn, supported by IMS. Like Three, EE sees the main VoWiFi benefit as improving coverage.

Unlike Three, however, the VoWiFi service from EE does not require customers to download an app, although firmware upgrades will be required on compatible devices (iPhones shipped with iOS 8 will natively support Wi-Fi calling).

In a recent global survey undertaken by Kineto, which describes itself as a supplier of Telco-OTT solutions, it was found that 16 per cent of mobile users in “key markets” said they had poor or no mobile voice coverage within their home.

The same survey discovered that 89 per cent of respondents with poor or no mobile voice coverage at home were also smartphone owners that had already configured their phone to connect automatically to a home WiFi network.

The firm argues that operator efforts to roll out IMS-based VoLTE will have the added benefit of addressing shortfalls in cellular coverage, since the same core network equipment also enables VoWiFi.