I am having trouble understanding the problem statement. You data was not enclosed in <code>..</code> tags and that is a problem. I don't really understand what removing the newlines in the 4th field means?

This is just a wild guess on my part - I guess that extra new lines meant spacers between these records - but maybe not?: 

use strict;
use warnings;

my $line;

while (<DATA>)
{
   chomp;
   if ( (/:$/../^\s*$/) =~ /^\d+$/) #exclude endpoint.
   {
       s/\s,\s/,/;
       $line .= " $_";
   }
   elsif (defined $line)
   {
       $line =~ s/^\s*//;
       print "$line\n";
       $line = undef;
   }
} 
print "$line\n" if defined $line; # just to be sure
                                  # all output is done

=prints
99~Arun~Kumar~Mobilenum: 1234-567,from Earth Human
98~Mahesh~Babu~Mobilenum: 5678-901,from Earth Human
98~Mahesh~Babu~Mobilenbbb: 5678-901,from Earth Human
=cut


__DATA__ 
99~Arun~Kumar~Mobilenum:
1234-567 , from Earth
Human


98~Mahesh~Babu~Mobilenum:
5678-901 , from Earth
Human

98~Mahesh~Babu~Mobilenbbb:
5678-901 , from Earth
Human

[download]
I guess something very, very simple like this is possible? 3 input lines to one output line? 
use strict;
use warnings;

my $input = do {local $/; <DATA>};
my @lines = $input =~ m/(.*\n.*\n.*\n)/g;
foreach my $line (@lines)
{
   $line =~ s/\n/ /g;
   $line =~ s/ , /,/g;
   print "$line\n";
}

=Prints
99~Arun~Kumar~Mobilenum: 1234-567,from Earth Human 
98~Mahesh~Babu~Mobilenum: 5678-901,from Earth Human 
98~Mahesh~Babu~Mobilenbbb: 5678-901,from Earth Human 
=cut


__DATA__ 
99~Arun~Kumar~Mobilenum:
1234-567 , from Earth
Human
98~Mahesh~Babu~Mobilenum:
5678-901 , from Earth
Human
98~Mahesh~Babu~Mobilenbbb:
5678-901 , from Earth
Human

[download]

In reply to Re: perl regex to match newline followed by number and text by Marshall
in thread perl regex to match newline followed by number and text by arunkumarzz

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.