If I remember correctly its actually in the Number:: family.. I think.. Anywho whatever module I saw it in, it went something to the effect of..

push(@data, '189803943', '39203', '12938032');

for ( @data ) {
    print "commified: " . add_c($_) . "\n";
}

sub add_c {
   my $n = shift;

   $n = '0' x ( length($n) % 3 == 2 ? 1 : 2 ) . $n if (length($n) % 3)
+;
   $n =~ s/(...)/\1,/g;
   $n =~ s/(?:^0+,?|,$)//g;
   return($n);
}
[download]

Produces:
commified: 189,803,943
commified: 39,203
commified: 12,938,032