Hi, I'm going got be in Australia for 1 month and want to use my 3G iPad. Can I just go to one of the carrier's retail shops and get a SIM and use a non Australian credit card to purchase one of the 30 data plans, then just not top it up when I leave? Or do you need an Australian address or Australian credit card? I really don't want to pay roaming by laving my home SIM in place. Thanks.