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 form 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 dissolves. Stir in low-fat buttermilk and evaporated milk; cover and chill.
Pour mixture into the 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.