In a cup, combine sugar and cinnamon. Set aside. Lightly brush butter on the inside of each taco shell. Sprinkle with sugar mixture, set aside. Remove cover from ice cream carton. To Slice Carton: Using a sharp knife, make a slit down the side of the carton, run knife around ice cream to loosen it; remove ice cream and place on a cutting board;cut in four slices. Cut each slice in half. Place each half in a prepared taco shell. Arrange ice cream taco's in a 13x9x2 inch baking pan. Cover tightly with plastic wrap or foil and freeze. At serving time, transfer tacos to a platter. Serve with a choice of toppings such as sliced strawberries, blueberries, whipped cream, chopped nuts, toasted coconut, chocolate or caramel sauce.