Hi. I am travelling to Europe and will be taking my Tri-band Digital mobile. My brother in law gave me his sim card that he used in Europe. You can buy them at any newsagency. They are a credit card with the simcard in them. Push the sim card out. THe phone number is imprinted on the card. They are usually prepaid. Much cheaper than roaming!!!! And you can pick up these practically anywhere in Europe aparently.
Try 'Orange' TOP UP
You must have a Tri-band or quad-band phone though, because of the different frequencies.