Larry Ives provides this usefull script to page Users when they've got dates in their calendar:

My users wanted to have their calendar events “pop-up” when the event time came about so I turned to my trust friend Perl and wrote a script. If anyone is interested it is free for the taking. (Use at your own risk) I put the script in cron which goes off every 5 minutes. It cycles though all of the users and looks for calendar events which are +/- 200 seconds from current Linux system time and sends an instant message to that user telling them about the event. You will need to have pop-up blocker turned off naturally. You will also need the Date::Calc and Net::Telnet modules for perl.

#!/usr/bin/perl -w
use Date::Calc qw(Mktime Today_and_Now);
use strict;
use Net::Telnet ();
 
my ($s, %nusrs, @mnums, $caltime, $m, $ldt, $hdt, $subj);
 
my @usrlist = ('user1', 'user2', 'user3');
my $user = 'admin';
my $pass = 'xxxxx';
my $fldr = 'calendar';
my $dt = Mktime(Today_and_Now());
# the cron is set to check for calendar events every 5 minutes
# so the script checks for events +/- 200 seconds
$ldt = $dt - 200;
$hdt = $dt + 200;
 
#logs in as admin (administrative account)
my $t = new Net::Telnet;
$t->open(Host => 'localhost', Port => 504);
$s = $t->getline;
$t->print("USER $user");
$s = $t->getline;
$t->print("PASS $pass");
$s = $t->getline;
 
# gets the password for each user
foreach (@usrlist)
{
 $t->print("GREG $_");
 $s = $t->getline;
 $s = $t->getline;
 $s = $t->getline;
 chomp($s);
 $nusrs{$_} = $s;
 for (my $int=1; $int<11; $int++)
 {
  $s = $t->getline;
 }
}
$t->print("LOUT");
$s = $t->getline;
 
# for each user the scripts checks their calendar events to
# see if there is one that is within 200 seconds +/-
foreach (@usrlist)
{
 $t->print("USER $_");
 $s = $t->getline;
 $t->print("PASS $nusrs{$_}");
 $s = $t->getline;
 $t->print("GOTO $fldr");
 $s = $t->getline;
 $s = $t->print('MSGS');
 $s = $t->getline;
 $s = $t->getline;
 
 do
 {
  chomp($s);
  push(@mnums, $s);
  $s = $t->getline;
 } until ($s == 000);
 
 foreach $m (@mnums) # loops through calendar messages (header and body)
 {
  $s = $t->print("MSG0 $m|1");
  $s = $t->getline;
 
  while (!($s =~ /^000/)) #  
  {
   if ($s =~ /^time=/)
   {
    my @ctime = split(/=/, $s);
    $caltime = $ctime[1];
   }
   if ($s =~ /^subj=/)
   {
    my @subject = split(/=/, $s);
    if (($caltime > $ldt) and ($caltime < $hdt))
    {
     $subj = $subject[1];
     print "$caltime $subj"; #
    }
   }
   $s = $t->getline;
  }
 }
 
# sends the chat message to the user with a current calendar event
$s = $t->print("SEXP $_|$subj");
$s = $t->getline;
$t->print("LOUT");
$s = $t->getline;
@mnums = ();
}
 
exit;