First off, the iPhone 4 will NOT work as a phone in Italy. The tower configuartion is different. What this means, is that you won't be able to send or receive text messages in Italy.
If you turn your wifi on, and turn your Global Data Roaming off, you should be able to access the Internet through WiFi (cafes, hotels, McDonald's) and check your e-mails, but texting is not going to be a possibility with your phone.
Thank you. I know I can' use it for phone calls, which is why I have subscribed to ICall. But I was not sure about text messaging. Now I know.
You should check out Skype for use over WiFi.
For texting download the textplus app, its a free texting app that works over wifi. It would be the best that u can do while over seas.