Luca wants to know which cell carrier would be good for a trip through Eastern Europe. Leo says that the EU will require free roaming across borders in all the EU states by 2017, but until then, it's a mixed bag. Dueche Telecom probably supports it.
Here's a good resource: prepaidwithdata.wikia.com. It will tell him all the carriers that support service in the countries he's traveling to. He should buy a SIM for the country he's visiting.