Optus has launched a new Voice over wi-fi (VoWiFi) service option that lets customers make calls and send messages seamlessly even when they are out of mobile coverage.
The telco launched its WiFi Talk service in 2015, through Android and iPhone apps. By comparison, WiFi Calling is a native service built into specific handsets and can switch customers away from Optus' 4G LTE mobile network automatically.
Although Optus said WiFi Calling is switched on for all its subscribers across Australia for no additional charge, technology caveats do limit the availability of the service and some of its features in some circumstances.
WiFi Calling requires support for Voice over LTE (VoLTE) as implemented by Optus on its network. Currently, only two handsets, Samsung's Galaxy S7 and S7 Edge, support Optus VoLTE and therefore Wi-Fi Calling.
It works on home networks and public hotspots, but not over virtual private network (VPN) tunnels. There may be public and corporate WiFi connections that have firewalls which prevent WiFi Calling from working - Optus does not guarantee that all WiFi connections will provide access to WiFi Calling.
Emergency calls to 000 can be made over WiFi Calling even when the device is out of mobile coverage. Such calls won't provide the location automatically to emergency services however. Optus said making emergency calls over the mobile network is preferred for that reason.
National Emergency Warning System (NEWS) short messaging service texts are not available over WiFi Calling either.
Around 100 to 120 kilobit per second of wi-fi bandwidth is required for Wi-Fi Calling to operate well. A five-minute call uses up about 3.8 MB, which will be zero-rated on Optus Fixed connections but not on other providers' networks, the telco said.
Optus said Wi-Fi Calling is encrypted between the handset and the mobile network, for both voice calls and messages.
Operators around the world have been disrupted by the appearence of so-called Over The Top (OTT) providers who offer voice and messaging services over data connections that bypass mobile neworks.
VoWiFi is an attempt by operators to stop OTT providers from cannibalising call and messaging revenue, effectively turning telcos into "dumb pipes" data networks.
Using wi-fi networks can also help reduce operator capital expenditure to improve customer experience, especially indoors in large buildings.