Pour milk into medium saucepan; sprinkle surface evenly with gelatin and let stand 10 minutes to hydrate gelatin.
Meanwhile, turn contents of two ice cube trays (about 32 cubes) into large bowl and add 4 cups cold water.
Measure heavy cream into a large measuring cup. With paring knife, scrape vanilla seeds into cream and place the pod in cream along with seeds; set aside.
Set eight 4-ounce ramekins on baking sheet; set aside.
Heat milk and gelatin mixture over high heat, stirring constantly, until gelatin is dissolved and mixture registers 135 degrees on instant-read thermometer, about 1½ minutes. Turn off heat, add sugar and salt; stir until dissolved, about 1 minute.
Stirring constantly, slowly pour cream with vanilla into saucepan containing milk, then transfer mixture to medium metal bowl and set the bowl over the ice water bath. Stir frequently until thickened to the consistency of eggnog and mixture registers 50 degrees on an instant-read thermometer, about 10 minutes. Strain mixture into large measuring cup and distribute evenly among ramekins. Cover baking sheet with plastic wrap; refrigerate until just set (mixture should wobble when shaken gently), 4 hours.
To unmold panna cotta, pour 1 cup of boiling water into a small bowl, dip one remekin at a time into the water, count to three, and lift the ramekin out of the water.
With a moistened finger, press lightly around the periphery of the cream to loosen the edges. Dip the ramekin back into the water for another three-count.
Invert the ramekin over your palm and loosen the cream by cupping your fingers between the cream and the edges of the ramekin.
Gently lower the cream onto the plate, drizzle with berry coulis and serve.