Optus has (rather quietly) officially announcedeSIM support for iPhone. Making them the first telco carrier in Australia to do so. Allowing existing, new, or re-contracting Postpaid mobile customers with an eligible iPhone to sign up to a plan using eSIM technology.
As Optus points out on their website, this will enable you to make and receive calls from two different mobile numbers. All without the need to swap SIMs or iPhones. Possible because the newest iPhones, the iPhone XS, iPhone XS Max, and iPhone XR support dual SIM with an eSIM. In other words, they have a slot for a physical SIM card and have an embedded SIM inside (eSIM).
At the time of writing, Optus is supporting eSIM with Postpaid (SIM only) plans only, with no support for pre-paid at this stage.
How to activate Optus eSIM
To sign up you will need to get an eSIM QR card to activate the eSIM and an eligible iPhone model running iOS 12.2 or newer. Optus states these are only available in stores. Selected stores will start to stock the QR cards from March 27, 2019. All stores will then receive stock by April 12, 2019.
Once you have the QR card, follow the below steps on your iPhone:
Go to Settings
Tap either Cellular or Mobile Data
Tap Add Cellular Plan
Use their iPhone to scan the QR code
For information on Optus eSIM can be found on their website. Or you can learn more, including how to use Dual SIM with eSIM on eligible iPhones at Apple Support.