One of the things you quickly learn if you travel to Europe or outside of the US, is that you can rack up some very hefty phone bills if you use your normal US phone. I am going to buy an inexpensive GSM phone that I found on Amazon.
You will also need a SIM card and there are a few options. You first have to make sure your get the right size SIM card – they come in a couple of sizes. This is a good reason to get the phone first to check the size it needs. Rick Steves has a great article on this topic – make sure you read it.