sub is_valid {
    # check to see if an entry consists of valid "phone number" chars.
    my ($phone) = @_;

    $phone =~ s/[\-\.\s\(\)]+//g; #remove punct. and spaces

    # return 1 if begins with digits and is followed by
    # Ext or ext or x and digits.
    return ( $phone =~ m/^\d+(?:(?:[Ee]xt)|x)*\d$/ );
}