If you’re planning to make calls in or to Italy, knowing the basics helps a lot. First off, the country code of Italy is +39. You’ll need to dial that when calling Italy from the US or anywhere outside the country.
Now, about local numbers — Italy uses area codes even for local calls. Yep, even if you're calling someone just a few blocks away, you still have to dial the area code for Italy, and don’t skip the starting zero (it’s part of the number).
Area codes vary by city. Rome is 06, Milan is 02, and Venice is 041. For mobile numbers, they usually start with 3 and don’t need a separate city code.
If you're using a foreign SIM, just dial +39, then the number including the zero. Pretty easy once you’ve done it once or twice.