code: def phone_numbers(self):
          
          if self._phone_numbers is None:
              self._phone_numbers = PhoneNumberList(self._version, service_sid=self._solution['sid'], )
          return self._phone_numbers
docs: Access the phone_numbers
  
          :returns: twilio.rest.proxy.v1.service.phone_number.PhoneNumberList
          :rtype: twilio.rest.proxy.v1.service.phone_number.PhoneNumberList