Pour boiling water over gelatin in large bowl; stir until gelatin is dissolved.
Add ice cubes; stir until gelatin begins to thicken.
Remove any remaining unmelted ice.
Add yogurt; beat with rotary beater until smooth.
Pour into dessert dishes, parfait glasses or molds.
Refrigerate until firm, about 45 minutes.
If desired, serve with a dollop of whipped topping on each.