Singtel mobile customers will soon be able to make phone calls using Wi-Fi through their phone's inbuilt dialler, without using apps such as Skype and WhatsApp.

The telco yesterday said it was rolling out its Voice-over-Wi-Fi (VoWiFi) service island-wide in August.

VoWiFi service will be available on any accessible Wi-Fi network, including those at home, in the office and Wireless@SG locations, regardless of the Internet service provider supplying the access on the Wi-Fi network.

"This will allow Singtel mobile users to make uninterrupted voice calls and text over Wi-Fi in locations such as basements and buildings over 20 storeys high," Singtel said in a statement.

The telco did not respond to queries on whether this service would be provided free or as a paid add-on to existing plans.

Making phone calls through Wi-Fi can help users cut down on their talktime minutes, which potentially saves costs should they go over their monthly talktime allocation.

Other telcos in Singapore say they would be rolling out their own VoWiFi services, too.

M1 said it would launch its service by the end of the year, while StarHub said it is monitoring how VoWiFi will work with its current HD voice service over the 3G and 4G networks before rolling out the service island-wide.

The VoWiFi rollout follows the results of a Heterogeneous Network (HetNet) trial conducted by local telcos and Internet service providers in collaboration with the Infocomm Development Authority (IDA) in the Jurong Lake District over the past year.

HetNet is a new wireless system that allows users to automatically switch between Wi-Fi and cellular networks, like 4G, in order to minimise surfing slowdowns and disruptions.

This way, a user making a call through VoWiFi can step out of range of the Wi-Fi network and continue the conversation without dropping the call as the phone will automatically switch to a cellular network.

Ninety per cent of those who took part in the trial had a better user experience, with faster speeds and smooth transitions between wireless and cellular networks, said IDA co-managing director Gabriel Lim.