code: private static List<String> convert(List<Recipient> recipients) throws PhoneNumberException {
  		List<String> tos = new ArrayList<>(recipients.size());
  		// convert phone numbers to international format
  		for (Recipient recipient : recipients) {
  			tos.add(toInternational(recipient.getPhoneNumber()));
  		}
  		return tos;
  	}
docs: Convert the list of SMS recipients to international phone numbers usable
  by OVH.
  
  @param recipients
  the list of recipients
  @return the list of international phone numbers
  @throws PhoneNumberException