In every country you visit in Europe you can buy an individual sim when you get there, which will work out much cheaper than almost any post paid plan with roaming enabled, without the risk of massive bills for excess data once you get home. But this can get a bit tiresome if you are going through multiple countries, getting a SIM in each one. It would be much easier if you could get one that worked in all the countries you were visiting....
What ever you do, don't buy one of those "Travel Sims", I'm yet to see one that includes much or any data.
The best pre-paid option I could find in Europe was pre-paid via three.co.uk. You can get a sim card on "pay as you go". Its killer feature is called "feel at home" where you can use the allowances they give you for use in the UK, in a number of countries in Europe, Asia and America. They also include Australia. To get this "feel at home feature" you have to buy an add on pack which converts your credit (which doesn't expire if you don't use it, into a pack that gives you a set amount of minutes, texts and data)
For 20 pounds you Get 3000 texts, 300 minutes plus all-you-can-eat data in the UK, or 12 gigs of data if you are roaming outside the UK. Thus for about $45 I got a sim that I can do virtually unlimited Facebook and blog updates, google map usage (which is a godsend when walking around in an unfamiliar city).
If your friends and family use iPhones, the call and sms limit is largely irrelevant, as you can call using FaceTime audio and use iMessage which all use your data instead. 12gigs is quite a lot for a month, normally at home I use less than 2 gig a month.
The only real "catch" is that to call an Australian or Italian number when using this SIM with "feel at home" enabled is that the call or sms cost aren't included in the pack, and cost 13p per minute or 5p per text. So just put 30 pounds credit on it, but a 20 pound add on pack which give you 12 gigs of roaming data, and 10 pounds remaining credit for the odd quick call back home or sms if you are or your are calling a non iPhone user.
If your not going to the UK first, you can find them on ebay and have them shipped to Australia.
Here is the details :-
http://www.three.co.uk/Store/SIM/Pay_As_You_Go
http://www.three.co.uk/Store/Pay_As_You_Go_Price_Plans
One issue is that you can't top them up without a UK credit card, but I found an online site that will let you purchase a recharge voucher without a UK credit card http://www.mobiletopup.co.uk
Both Sharon and I have these SIMs, Paul didn't have one, so we just got him one at the first mobile shop we went past, also happened to be "Three", (http://www.tre.it/tariffe/all-in-200-extra). This one cost 30 euro and came with 2 gig of data for the month, which is renewable for 10 euro a month
Can't be bothered buying a SIM especially for Europe ?
Telstra prepaid SIMs have global roaming enabled where you can make calls and send texts, but its not cheap. Its a few dollars a minute for a call, or about 70c a text. Data is $10 a megabyte.
If you don't mind just using wifi only (turn the data off from the settings), this is a good option to have a phone for emergency or quick calls, plus the odd SMS.
