If that's your entire code you're missing a couple of things like the open() and login() methods.

Not sure the purpose of the serverid hash with a single key\value, but here's what the code should be with a hash:

use strict;
use warnings;
use Net::Telnet;

my ($username, $password)=("benlaw", "usertesting");

my $serverid{'testsvr1'} = '10.159.32.21';

my $t = new Net::Telnet (Timeout => 10,
                      Dump_Log=> "err_dump.log", 
                      Output_log=> "err_out.log",
                      Prompt => "/\$\s/" );
my @date;

while ( my ($key,$value) = each(%servid){

  $t->open($key=>$value);
  $t->login($username,$password);
  @date = $t->cmd("date");
  print @date;
  $t->close;
}
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Here's the way I would write it if I had a single server to log into:

use strict;
use warnings;
use Net::Telnet;

my ($username, $password)=("benlaw", "usertesting");

my $serverid = "10.159.32.21";

my $t, @date;


$t = new Net::Telnet (Timeout => 10,
                      Dump_Log=> "err_dump.log", 
                      Output_log=> "err_out.log",
                      Prompt => "/\$\s/" );

$t->open($serverid);

$t->login($username, $password);

@date = $t->cmd("date");

print @date;

$t->close;
[download]