[regex] What regular expression will match valid international phone numbers?

public static boolean validateInternationalPhoneNumberFormat(String phone) {
    StringBuilder sb = new StringBuilder(200);

    // Country code
    sb.append("^(\\+{1}[\\d]{1,3})?");

    // Area code, with or without parentheses
    sb.append("([\\s])?(([\\(]{1}[\\d]{2,3}[\\)]{1}[\\s]?)|([\\d]{2,3}[\\s]?))?");

    // Phone number separator can be "-", "." or " "

    // Minimum of 5 digits (for fixed line phones in Solomon Islands)
    sb.append("\\d[\\-\\.\\s]?\\d[\\-\\.\\s]?\\d[\\-\\.\\s]?\\d[\\-\\.\\s]?\\d[\\-\\.\\s]?");

    // 4 more optional digits
    sb.append("\\d?[\\-\\.\\s]?\\d?[\\-\\.\\s]?\\d?[\\-\\.\\s]?\\d?$");

    return Pattern.compile(sb.toString()).matcher(phone).find();
}