I want to use my iPhone 6 in Europe (Italy)

I'd like to use it for about 3 weeks. I want to be able to make local, in-country calls as well as calls to/from the US. I know VZN offers an international plan but I'm not certain how I would use that while I'm there. Can I call local numbers? Do I give businesses/restaurants my US number and make them call an international number to reach me?  What are the advantages of doing that over getting a SIMM card in country? And does the SIMM card reset everything on my phone?