Considering the data you need, there is no way for you to avoid storing the phone numbers, then outputing them when you find the reason. You could leave the elements (and just these elements) in the tree though, by using twig_roots to get the twig built only for them:

#!/usr/bin/perl

use strict;
use warnings;

use XML::Twig;

XML::Twig->new( # the twig will only contain PHONENO/ENTRY and REASON/
+ENTRY elements
                # (plus the root or it would not be a tree)
                twig_roots => { 'BL_USER/PHONENO/ENTRY' => 1,         
+     
                                'BL_DPLI_RECORD/REASON/ENTRY' => \&rea
+son,
                              }
               )
         ->parsefile( 'phone_data.xml');

sub reason
  { my( $t, $reason)= @_;
    foreach my $phone_no ($reason->prev_siblings)
      { print $phone_no->text, ";", $reason->text, "\n"; }
    $t->purge;
  }
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i have some questions left to understand this.
with twig_roots it will make me an array if more then 1 entry is presented ?
$reason->prev_siblings points to that array so the script process it one by one
what means prev_siblings ?
kd ultibuzz

twig_roots doesen't make an array, it makes a tree, with the document root as the root, and the elements listed in the hash as first children. Then the descendants of those elements compose the rest of the tree. prev_siblings means previous siblings. When you get a reason element, at that poit the tree is made of the root, with the phone elements as children, and the reason element as the last child. $reason->prev_siblings will then return the list of phone numbers. Once you're done printing them, you can get rid of them through the purge method, so they don't interfere with the processing of the next set of data.

Does it make sense?