Combine boiling water and coffee granules; stir well. Cover and chill.
Combine sugar, salt, and egg substitute in a bowl; beat at medium speed of a mixer 3 minutes or until sugar is dissolved. Add coffee; beat 2 minutes. Add milks; beat well.
Pour mixture into the freezer can of a 2-quart ice-cream freezer; freeze according to manufacturer's instructions. Spoon into a freezer-safe container; cover and freeze for at least 1 hour.