Last year Apple brought Dual SIM support to the new iPhones, including the iPhone XS, iPhone XS Max, and iPhone XR. A feature which allows you to have two cellular services and plans connected to the iPhone.
For example, you may choose to have the primary service be your personal number. While an additional service is one you use for work.
However, Apple has enabled this feature by using a relatively new technology called eSIM. A SIM-card that is embedded inside the iPhone and cannot be removed. It is the same type that Apple uses inside the cellular versions of the Apple Watch and the new iPad Pro.
The benefits of eSIM include being able to choose a carrier and plan on the go. It will even be possible to have a plan with a different provider to your primary plan. No need to go to a retail store to buy a SIM. The downside of this, however, is it relies on carriers to support the feature first. And this is where the issue begins.
At this stage, all three carriers in Australia have not brought eSIM support for the iPhone to their customers. This includes Optus, Telstra, Vodafone, and any provider that runs off their network. And there is no official word on when they will, although Vodafone has apparently been testing the feature for some months now.