Slice tops off 4 small cantaloupes. (Save tops) Scoop out insides, blend cantaloupe with 1 cup water. Stir in orange juice concentrate. Pour fruit mixture into a 9x9x2 inch pan. Cover and freeze 6 hours or until you are ready to eat. Let frozen mixture soften about 10 minutes. With apple corer, punch straw holes in the melon tops. Spoon fruit mixture into melons. Fill with chilled lemon-lime carbonated beverage or flavored seltzer (one or two 12 ounce cans).