You didn't say what part of it your team is having difficulty understanding, so here's a basic rundown of what is going on:

sub get_abandonned($) {                                # Subroutine de
+finition.
  my $dnis = shift;                                    # $dnis will ho
+ld
                                                       # the parameter
+.

  my $total = 0;                                       # $total holds 
+0.

  for my $key(keys %all_calls) {                       # There is a ha
+sh named
                                                       # %all_calls.  
+Iterate
                                                       # over the keys
+ of the
                                                       # hash and assi
+gn each
                                                       # key to $key o
+n its
                                                       # respective it
+eration.

    next if ($key =~ /duplicate/);                     # Proceed to ne
+xt
                                                       # iteration if 
+the
                                                       # current key c
+ontains
                                                       # the text 'dup
+licate'.

    if(                                                # If all of the
                                                       # following are
+ true:
         $all_calls{$key}->[DNIS] eq $dnis
      && $all_calls{$key}->[SPEECH] == 0
      && $all_calls{$key}->[TRANSFER] eq "hungup"
    ) {                                                # then do the f
+ollowing:

      my $time_length                                  # Give a value 
+to
                                                       # time_length,
        = &get_call_length($all_calls{$key}->[TIME]);  # from this fun
+ction
                                                       # call.

      if($time_length <= -29) {                        # Now if this i
+s true...
        $total++;                                      # increment $to
+tal.
      }
    }
  }                                                    # Move on to ne
+xt key.
  return $total;                                       # return the $t
+otal.
}
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