Melt margarine in large nonstick saucepan over medium heat. Add onion; cook and stir until tender. Stir in flour; cook 1 to 2 minutes, stirring constantly. Gradually stir in broth and apple juice.
Add squash, curry powder and rosemary; mix well. Cook over medium-high heat until mixture begins to boil, stirring occasionally. Reduce heat; simmer 10 minutes to blend flavors.
To serve, ladle soup into 6 individual soup bowls; top with yogurt. If desired, garnish with fresh rosemary sprigs.