If you intend on travelling outside city areas, you should look at a Telstra sim as these offer you the ideal coverage in rural Australia. The Australia Post shop while in the departures hall of T1 sells Telstra sim cards. You can also find several private counters marketing all brands. https://sydneydomesticairportlimo63715.look4blog.com/65315514/little-known-facts-about-sydney-domestic-airport-limousine