In medium bowl, combine margarita concentrate, tequila and lime juice; mix well. Spread mixture in 8-inch square (2-quart) glass baking dish. Freeze at least 5 hours or until set.
To serve, run lime wedge around rim of each glass; dip in margarita salt. For each drink, spoon 2/3 cup frozen mixture into glass; pour 1/4 cup carbonated beverage over top. Garnish with lime wedges.