Using lime wedges, moisten the rims of 6 margarita or cocktail glasses. Set aside lime wedges for garnish. Sprinkle sugar on a plate; hold each glass upside down and dip rim into sugar. Set aside. Discard remaining sugar on plate.
Scoop ice cream and sherbet into prepared glasses. Combine soda, lime juice and tequila; pour into glasses. Garnish with reserved lime wedges. Serve immediately.