A list of CallingPoint objects.

        This is the list of all previous calling points for the service,
        including all associated services if multiple services join together
        to form this service.

def previous_calling_points(self):
        """
        A list of CallingPoint objects.

        This is the list of all previous calling points for the service,
        including all associated services if multiple services join together
        to form this service.
        """
        calling_points = list()
        for cpl in self._previous_calling_point_lists:
            calling_points += cpl.calling_points
        return calling_points