Two approaches seem logical to me. First, similar to yours, based on regular expressions. I would slurp in the data in one go though and then replace superfluous pieces, like this: 

use strict;
use warnings;
my $data;
{
        local $/;
        $data=<DATA>;
}
$data =~ s/\n\s*\n(From: |To: |User-Agent: )/|/g;
$data =~ s/Arrival Time: ([^|]*\|[^|]*\|[^|\n]*)\n/$1|--\n/g;
print "Arrival Time|From|To|User-Agent\n\n";
print $data;

__DATA__
Arrival Time: May 2, 2013 10:37:50.813000000

From: <sip:639gwhuaping01-14@119.38.228.43>;tag=70c8b229-1c

To: <sip:639gwhuaping01-14@119.38.228.43>

Arrival Time: May 2, 2013 10:38:05.274000000

From: <sip:639gwhuaping01-01@119.38.228.43>;tag=70c8b229-2

To: <sip:639gwhuaping01-01@119.38.228.43>

Arrival Time: May 2, 2013 10:38:05.451000000

From: <sip:639gwhuaping01-11@119.38.228.43>;tag=70c8b229-16

To: <sip:639gwhuaping01-11@119.38.228.43>

User-Agent: Quintum/1.0.0 SN/0030E130409A SW/P108-09-10

[download]

Alternatively, and probably easier to maintain, is to read the data into a hash and print/empty whenever a dataset is complete, like this (with the same __DATA__ segment as above): 

use strict;
use warnings;

sub printdata {
        my $data = shift;
        $$data{"User-Agent"} //= "--";
        print join "|", @$data{ ( "Arrival Time", "From", "To", "User-
+Agent" ) };
        print "\n\n";
        %$data = ();
}

my %data;
my ($item, $value);
print "Arrival Time|From|To|User-Agent\n\n";
while(<DATA>){
        chomp;
        next unless ($item, $value) = /^(.*?): (.*)/;
        printdata \%data if $item eq "Arrival Time" and %data;
        $data{$item} = $value;
}
printdata \%data;

__DATA__
Arrival Time: May 2, 2013 10:37:50.813000000
...

[download]

In reply to Re: Arranging multiple lines by hdb
in thread Arranging multiple lines by r2ro

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