[1] Australians with soon be able to hold voice calls using a home Wi-Fi network for Optus and Vodafone.
[2] Optus and Vodafone spokespeople confirmed to Good Gear Guide that the Wi-Fi calling support in Australia is coming, with Optus expected to announce its commencement by “mid-2015”.
[3] Users will have the flexibility to switch onto a home Wi-Fi network when cellular reception is weak or alternate between the two networks during an active phone call.
[Source] Australian Information Technology News – Optus, Vodafone bringing Wi-Fi Calling to Australia