Wi-Fi calling allows Optus customers using certain 4G phones to make calls even when there is no signal.
VoLTE (Voice over Long-Term Evolution) is a feature of the 4G mobile system that essentially treats voice calls as if they were data. It’s similar to how VoIP allows voice calls to be transmitted over the internet.
VoLTE can be further extended to transmit calls over the internet when the phone connected by Wi-Fi – which is known as VoWi-Fi (Voice over Wi-Fi).
This capability is now available to Optus's post-paid consumer and business customers.
The first phones supported by Optus are the Samsung Galaxy S7 and Galaxy S7 Edge, but the list is expected to grow. Carriers in other countries already support VoWi-Fi on the iPhone 6 and later, and Galaxy S5 and later.
It's not clear whether Optus is actively preventing other handsets from being used, or if it just that the company won't provide any assistance for owners of phones that aren't on the 'supported' list.
An important point is that the user doesn't have to take any special action to use VoWi-Fi apart from the initial set-up. Once that's done, everything happens automatically.
“When Wi-Fi calling is switched on, the device automatically detects and seamlessly switches to an available Wi-Fi connection to use voice and messaging services,” said Optus Networks acting managing director Dennis Wong.
As Optus points out, it needs "a strong and reliable Wi-Fi connection with a bandwidth of around 100 -120kbps" and some Wi-Fi networks may block VoWi-Fi traffic.
VoWi-Fi can be used to make or receive calls, SMS and MMS within Australia, which are charged the same way and at the same rates as normal use.
VoWi-Fi data is not charged or counted for Optus fixed broadband customers, but it will be included by other internet service providers. Optus says a five-minute call uses about 3.8MB of data, so that's unlikely to be much of a problem unless you already come close to your quota or have several people each spending a lot of time on the phone.