I agree. A quick backup, then jailbreak. A quick google search will find numerous tutorials. You can also look on youtube for video guides. I'd recommend picking up an Optus or Telstra 'sim pack' when you get to Australia. They have coverage pretty much everywhere and will include credit when you purchase them. Pretty much every shopping center will have on of the two, if not both, in them. They usually range from $10-$30 AUD, and generally come with that amount of credit. Watch out for data costs though, they can get pretty high.