That's fine, but it is a Hash of Hash (HoH), not a Hash of Array (HoA). You should perhaps take a look at Data::Dumper.

use strict;
use warnings;
use Data::Dumper;

my $rboc    = "SA";
my $telco   = "0009";
my %HoH;
my %MultiHash;

$HoH{$rboc}{$telco} ++;
$MultiHash{$rboc, $telco} ++;

print Dumper (\%HoH);
print Dumper (\%MultiHash);
[download]

Prints:

$VAR1 = {
          'SA' => {
                    '0009' => 1
                  }
        };
$VAR1 = {
          'SA0009' => 1
        };
[download]

Note that there is a hidden character in the 'SA0009' string!

Update: added second method.