Italy is famed for it's gelato. We might call it "ice cream" but it's so much more than that. It's richer and creamier without being heavier. The flavours are more intense and most of the gelateria make theirs by hand, churning goodness into every lick of it!
We were in Rome for 5 days though only managed to get to two places. We did have some for dessert at one or two restaurants but it doesn't quite seem the same as sitting in a square by a beautiful fountain in the sun or as the sun is going down, with a cone or a cup of gelato in your hand. You may pay more in the hot tourist areas such as Piazza Navona or Rotunda but even then, it doesn't matter because it's all part of the Rome experience.
Most of the shops I've seen are small, just room enough for the counter and one or two people. The rest line up out the door it seems. You can usually choose at least 2 flavours or more. Some shops sell it by cups of varying sizes and you can fit in as many scoops as you can, usually 2 or 3 at least and the fun is in picking various flavours and seeing if they all work together.
We had gelato from a small outlet in Piazza Navona. It wasn't the more famed Tre Scalini, which is also a restaurant, it was just a tiny storefront across from the big church and Fountain of Four Rivers, I seem to recall. We also tried some from a shop called Blue Ice which is a chain of gelateria. The one we went to is close to the Piazza del Risorgemento outside the Vatican walls at the end of Via Ottaviano. Other famed locations are near the Pantheon and Trevi Fountain, naturally, because of the throngs of tourists that visit there but you can find a gelato shop anywhere in Rome easily. And you should.