<?php
 function format($n, $v = 1 ) {
   if ($n < 900) {
 	$format = number_format($n, $v);
 	$forma = '';
   } else if ($n < 900000) {        
 	$format = number_format($n / 1000, $v);
 	$forma = 'k';
   } else if ($n < 900000000) {
 	$format = number_format($n / 1000000, $v);
 	$forma = 'M';
   } else if ($n < 900000000000) {
 	$format = number_format($n / 1000000000, $v);
 	$forma = 'B';
   } else {
 	$format = number_format($n / 1000000000000, $v);
 	$forma = 'T';
   }
   if ($v > 0) {
 	$script = '.' . str_repeat( '0', $v );
 	$format = str_replace( $script, '', $format );
   }
 return $format . $forma;
 }

#Usage
$number = '10000';
echo format($number); / return 10k
?>