Sorry just coming to this party a bit late, if you are with Telstra and most Australian networks do offer a service for coverage within Europe.
However, be warned it can work out very pricey. What most of my Aussy colleagues do is simply, as you wish to speak to one another within the same city is stick with the text service, (works fine in Western Europe) and text over the number of the nearest fixed line or mobile for voice calls. Texts can also add up, but once you have sent the numbers switch them off.
Or once in the UK, France & Italy if you are here for sufficient time I would suggest you opt for pay-as-you go sim cards which easy to purchase for voice service. You will require an unlocked phone, but forget about internet service – its expensive here just stick with text.