code: def available_phone_numbers(self):
          
          if self._available_phone_numbers is None:
              self._available_phone_numbers = AvailablePhoneNumberCountryList(
                  self._version,
                  account_sid=self._solution['sid'],
              )
          return self._available_phone_numbers
docs: Access the available_phone_numbers
  
          :returns: twilio.rest.api.v2010.account.available_phone_number.AvailablePhoneNumberCountryList
          :rtype: twilio.rest.api.v2010.account.available_phone_number.AvailablePhoneNumberCountryList