Yes if you are an ATT subscriber
I have used an iPhone 3G and 3GS in rome on a number of trips. As soon as you arrive at Leonardo Da Vinci you will receive a series of text messages from the local providers soliciting your business. Chose any one - you can always change later.
Remember to subscribe to a foreign calling plan before departure and turn off roaming when you arrive. I generally activate roaming 3 times per day to check email etc. morning noon and just before dinner.
I hope this helps