code: public final String formatCommonNational(final PhoneNumberInterface pphoneNumberData) {
      final StringBuilder resultNumber = new StringBuilder();
      if (isPhoneNumberNotEmpty(pphoneNumberData)) {
        PhoneCountryData phoneCountryData = null;
        for (final PhoneCountryCodeData country : CreatePhoneCountryConstantsClass.create()
            .countryCodeData()) {
          if (StringUtils.equals(country.getCountryCode(), pphoneNumberData.getCountryCode())) {
            phoneCountryData = country.getPhoneCountryData();
            break;
          }
        }
        if (phoneCountryData == null) {
          return null;
        }
        resultNumber.append(phoneCountryData.getTrunkCode()).append(' ');
        resultNumber.append(this.groupIntoParts(pphoneNumberData.getAreaCode(), 2));
        resultNumber.append(" / ");
        resultNumber.append(this.groupIntoParts(pphoneNumberData.getLineNumber(), 2));
        if (StringUtils.isNotBlank(pphoneNumberData.getExtension())) {
          resultNumber.append(" - ");
          resultNumber.append(this.groupIntoParts(pphoneNumberData.getExtension(), 2));
        }
      }
      return StringUtils.trimToNull(resultNumber.toString());
    }
docs: format phone number in Common national format.
  
  @param pphoneNumberData phone number to format
  @return formated phone number as String