Vonage's Terms of Service are a littly sketchy on whether you can use their service or not in another country:
"2.6 Use of Service and Device by Customers Outside the United States. Although we encourage you to use of the Service to place calls to foreign countries from within the United States, we do not presently offer or support the Service in any countries other than the United States and Canada. If you use the Service or the Device outside of the United States or Canada, you will be solely responsible for any violations of local laws and regulations resulting from such use. We reserve the right to terminate your Service immediately if we determine, in our sole and absolute discretion, that you have used the Service or the Device outside of the United States or Canada."
Note they say they do not offer and support the service, but if you use it, you are liable for blah, blah, blah. Obviously it should work. Is it legal is another question. The above pretty much absolves them I guess of what people do with their phones. But I also found this on the Vonage website:
"I also found another interesting use for Vonage: tote it with you to Europe. Although you may have a tough time finding somewhere to hook it up, it will work. And anyone who has ever visited or lived in Europe knows that international calls are much more expensive there than they are in the US. So I suggest you take your Vonage along with you and stay in a hotel with Internet access. Vonage's international rates are going to be lower than the hotel's, but the real advantage comes when you call the US. These calls are completely and entirely free, because, as far as Vonage is concerned, it is a US to US call--your actual physical location does not matter"
This was published by a third party, but it still is on their site. If anyone is using a Vonage phone in Italy I would appreciate your feedback/comments.