tie(my %cal, etc) or die "cal: $!\n";
tie(my %addr, etc) or die "addr: $!\n";

$cal{"cal_$key"} = $cal_value;
$addr{"addr_$key"} = $addr_value;
# later

for ( sort { $a <=> $b || $a cmp $b } keys %cal, keys %addr) ) {
   if (m/^cal/) {           # its from the calendar
   } elseif ( m/^addr_/ ) { # from the address book
   } else {                 # where did this come from?
   }
}