[Motel75]

I'd have to disagree with the international SIM business; it sounds like you're mostly going to be in Italy, in which case an Italian SIM would make a lot of sense.

I've had good results with Vodafone, and if you're interested in coming back, keeping the SIM active means only a 3 euro topup every 10 months, which you can do on their website using a foreign credit card (basic Italian required, however). The Passport option would make sense for placing calls in the other countries; you might be able to use it with your Australian SIM.

Receiving calls is another matter, and you might want to have a look at the rates for using your Australian SIM vs. those for the Italian one while outside of Italy. However, if you're only keeping the phone in case of emergency calls, this shouldn't be such an issue.

Remember that to get an Italian SIM you need a real or fake codice fiscale; see the Italy page for details, and a codice fiscale calcuator. (I figured mine out a few years ago using pen and paper, and used that; when I finally got a real one, which took 10 minutes, it was only slightly different because they included my middle name.)