This is a wrinkle on what everyone said above. While there are now no roaming charges for phone calls, data mostly does not carry over from country to country. Thus, in May, I bought a sim card through Vodafone in Portugal. When I hit Spain, I was able to make phone calls without roaming charges. HOWEVER, only 100 mb of data -- very little -- carried over. So, I bought a new sim card in Spain through Orange. Same thing happened later in June, when I flew from Santiago to London. No roaming charges for phone calls, but very little data carryover. Thus, if you're going to be counting on your phone's ability to connect to the data network, you'll need to get a new sim card in every country. (Even without a data connection, though, you'll still be able to access wi-fi).