To call Italy from the United States, dial the international prefix, 011; then Italy's country code, 39; and then the city code (for example, 06 for Rome and 055 for Florence), which is now built into every number. Then dial the actual phone number.
To call from one city code to another, dial the city code, complete with initial 0, and then dial the number. (Numbers in Italy range from four to eight digits. Even when you're calling within the same city, you must dial that city's area code -- including the zero. A Roman calling another Rome number must dial 06 before the local number.)
To dial direct internationally, dial 00 and then the country code, the area code, and the number. Country codes are as follows: the United States and Canada, 1; the United Kingdom, 44; Ireland, 353; Australia, 61; New Zealand, 64. Make international calls from a public phone, if possible, because hotels charge inflated rates for direct dial -- but bring plenty of schede (change). A reduced rate is applied from 11pm to 8am on Monday through Saturday and all day Sunday. Direct-dial calls from the United States to Italy are much cheaper, so arrange for whomever to call you at your hotel.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.