Australian Telstra Prepaid SIM Activation Summary
UPDATE:
The main problem with Telstra is activation prior to arrival in Australia.
Our best alternative is the OPTUS SIM (see info here), which provides better value for money and can be activated online prior to entering Australia (they let you verify your ID by using any international credit card).
See still have our full step-by-step guide to activating a Telstra SIM here, but recommend to only do this if you don't want to activate it prior to arrival (if you don't have an Aust ID), or if you have an Aust ID it will be fine to activate prior to arrival.