The first two things you need to make sure of is that your phone supports the European cellular frequencies which are 900mhz/1800mhz and optionally 2100mz. Go to ATT's website and see if the phone is listed as a world phone or lists these frequencies. Alternatively, there is a database over at phonescoop.com with this information. The second thing you need to do is make sure that international roaming is active. You are best calling ATT's international customer service at 1-800-335-4685 or 1-916-843-4685. If you have Skype, you can call the US 800 number for free over the internet. If you are calling from the hotel phone, you'll need to call the 916 number. Have the hotel phone number handy because they will call you right back. 90% of the time this cures the problems. Every now and then there is a problem on the backend that Customer Support will need to straighten out.