# you call it with the length, a refernce to your
# character Array and a string thats already done
sub combine {
        my($length,$chars,$ready)= @_;
        my($char);
        # First test whether or not we have to add chars
        if ($length) {
                # if so we iterate through the chars
                foreach $char (@$chars) {
                        # and call combine
                        # recursively by decrementing the
                        # level and adding one char to
                        # the chars we already have
                        combine ($length-1, $chars, $ready.$char);
                }
        }
        else {
                # if there is nothing left to do,
                # we simply print the result.
                # we could also push it to a global
                # array for later processing
                print $ready,"\n";
        }
}

# this is the first call
@chars=qw(0 1 2 3 4 5 6 7 8 9 # *);
combine (2, \@chars, '');
[download]

> how long should the numbers be?

hehe , arbitrary :)

the onleliner above got used in the dtmf-project
(wich lost its glory after listening in to random dtmf sequences for about 2 hours;)
but i did copy this one to my wiki, ...
really handy to have laying around for future usage, thx :) (++;)