#!/usr/bin/perl

use warnings;
use strict;

open my $fh, '+>', 'output.txt'
  or die("Can't open the damn file!: $!");

while(my $line = <DATA>){
    chomp $line;
    my ($name, $num) = split(/\s+(?=\d)/, $line);

    # some lines have whitespace after the num

    $num =~ s/\s+//g;

    if ($num =~ /^\d{4}$/){
        $num = "(333)-321-$num";
    }
    elsif ($num =~ /^\d{3}-\d{4}$/){
        $num = "(333)-$num";
    }

    print $fh "$name $num\n";
}

__DATA__
Black, Joe 0987
Smith, Sue 0534
Brown, Andy 587-0986