STIR boiling water into combined gelatin and sugar in large bowl at least 2 minutes until completely dissolved. Stir in club soda. Pour into 9-inch square pan; cover.
FREEZE about 1-1/2 hours or until ice crystals form 1 inch around edges. Spoon into blender container; cover. Blend on high speed 30 seconds or until smooth. Return to pan; cover.
FREEZE 6 hours or overnight until firm. Scoop into dessert dishes. Store leftover sorbet in freezer.