Your phone is eSIM compatible (both a traditional physical chip SIM and a software programmable eSIM). Plus Optus also supports “wifi calling” so you should be able to make/receive calls and text over wifi (just make sure “roaming“ is turned off to avoid it using data).
If your current Optus service is using a physical SIM, then two options:
1. Find a suitable eSIM provider - many / most will cover multiple countries regions or allow you to buy coverage for each country. They can provide cheap access to data when travelling. They’re generally easy to install and use via an app and some iPhone settings.
Some useful info and discussion here:
I am interested in the concept of eSims but have no experience with them. The notion of running my local sim plus having an international sim for phone use while in USA and EU could be handy. What have members experience been? TIA
www.australianfrequentflyer.com.au
2. if you prefer physical pre-paid SIMs for each country or region, then you can switch your Optus service to the eSIM and that frees up the physical slot for roaming SIMs. Some people like this option because they already have SIMs.