This is something everyone should do while in Rome. Eating gelato is nearly a god-given right in Italy and Gelateria’s abound all over the city. This is a summary taken from the complete article which can be found here.
Not every gelato shop will offer both cups and cones, but the vast majority will. The word for cup is “coppa” (KOH-pah) and cone is “cono” (KOH-noh). You’d ask for either “una coppa” or “un cono,” but the fun doesn’t end there. Sometimes, you’ll see several different kinds of cones on display, so be prepared to point to the one you want.
Unlike in some ice cream shops outside Italy, the size of the cup or cone you’re getting doesn’t pre-determine how many scoops of gelato you’ll get. I’ve seen people cram three flavors into even the smallest cups. So after you’ve chosen the vessel for your gelato, you’ll need to say how many scoops you’d like. In Italian, the word you’ll use is “gusti” (GOO-stee), which literally means “flavors.” So technically you’re telling them how many flavors you’d like, and they’re going to give you one scoop per flavor. Make sense? Good!