If I buy a iTunes card in Europe, Holland, could I (or anyone who has the key) use it in Australia?
iTunes Gift Cards will only work in the same country they were bought in.
iTunes Gift Cards are not available in Luxembourg, Portugal, or Greece. Gift recipient must have or open an iTunes Store account in the same country as purchaser to redeem gift. The iTunes Store is available only to persons age 13 or older in the U.S. and many other countries; see http://www.apple.com/support/itunes/ww for a list of countries. Requires iTunes 6.0 or later (7.0 or later for video), compatible hardware and software, and Internet access (fees may apply). Terms apply. See http://www.apple.com/itunes/store for more information.
Of course, if you buy a card for yourself, you’re both the purchaser and the recipient. So only buy iTunes Gift Cards in countries where you have an iTunes Store account.
I once had the same thing. My girlfriend bought me a iTunes Gift Card in The Netherlands, but since we live in Belgium, I couldn't use it. So I contacted Apple and the responded:
Michiel, unfortunately, gift cards and gift certificates are redeemable only on the iTunes Store for the country for which they were purchased. International gift exchanges are not allowed.
I know that is disappointing, and I do apologize for the inconvenience, but perhaps your friend would like to give the card to someone who lives in The Netherlands, or use it herself.
Please do not hesitate to let me know if you have any further questions, Michiel, and I will gladly assist you further. Have an awesome day and thanks for being a part of our iTunes family.
iTunes Store Customer Support