Hi lilywhite,
No problem. If you ask whoever is buying it for you to ask the shop or have a look on the box regarding the voltage.
As for the warranty as long as you have a US address you will be fine.
However you should also remember that should you need to have your PS3 replaced/fixed then some significant additional charges to yourself will be incurred because you will need to send your PS3 to the US.
Remember you will need to pay to have it shipped to the US and back again and this can be an expensive excercise depending on who and how you choose to have it sent, plus insurance.
As an example with my PS3 (which now sits broken and useless) i purchased mine on a small carribean island just 3 hours flight from Miami.
I asked Sony to send the repair box to a friend in the US who then forwarded the empty repair box to me via Fed-ex and it cost 150 USD for an empty box!...and i was relatively close to the US
I never proceeded any further because the expense was outrageous.
As you can see although Sony wont charge you for the replacement / repair there can be significant other charges involved.
Remember:
1. You will have to pay shipping to have it sent to the US and back again. I would recommend you check with Australia Post, DHL, Fed-Ex on their rates for sending a 7kg package from Australia to the US
2. You will need to check with customs on how to avoid
22 hours ago
Gold Coast - Queensland