Scrape seeds from vanilla bean; place seeds and bean in a medium saucepan. Pour 2% low-fat milk into pan; cook over medium-low heat to 180° or until tiny bubbles from around edge of pan (do not boil), Remove from heat; discard vanilla bean. Pour vanilla-milk mixture into a large bowl, and add sugar, stirring until sugar disolves. Stir in low-fat buttermilk and evaporated milk; cover and chill. Pour mixture into freezer can of an ice-cream freezer, and freeze according to manufacturer's instructions. Spoon ice milk into a freezer-safe container; cover and freeze at least 1 hour.