The only thing that matters is the ROM version on your device. For example, if your firmware is an unbranded UK variant, you will get the update when Nokia releases it for the UK, no matter where in the world or on what carrier you are. If you've got a UK Vodaphone variant, you will get the update after Vodaphone has tested the firmware on their network and gives Nokia the permission to distribute the update on their network. Again, you would receive it then, no matter where in the world you actually are.
So for you, assuming the device you bought in SA also came with SA firmware, and that it is an unbranded device, you will get the update when Nokia releases the update for SA.