Microsoft has already commenced the roll out of the Windows 10 Mobile operating system for existing Windows Phone 8.1 devices -- you can check out the list of compatible devices here. The new operating system is set to roll out for carrier-bound devices in some markets as well.
Vodafone Australia has updated its software update support page list a number of Windows Phone 8.1 devices which will receive the latest Windows 10 Mobile operating system tomorrow, that is, March 25th (via Windows Central). It includes Lumia 930, Lumia 735, Lumia 640 and Lumia 640 XL.
Windows 10 Mobile brings a number of enhancements and new features such as Hello Cortana, and Continuum and Windows Hello, for phones that provide those capabilities. So if you're living in Australia and own any of the above-mentioned Windows Phone devices tied to Vodafone, you can expect to try out the new operating system on your handset.