code: @ToString
      public String toE164NumberWithExtensionString() {
      	
      	StringBuilder formattedString = new StringBuilder(toE164NumberString());
      	
      	if(number.hasExtension()) {
      		formattedString.append(RFC3966_EXTN_PREFIX);
      		formattedString.append(number.getExtension());
      	}
      	
      	return formattedString.toString();
      }
docs: {@inheritDoc}