<?php
$numbers=array('+7(911)-506 56 56',
               '8-911-50-656-56',
               '89115065656',         
               '02',
               '8-(9)_115  _065 6-3-5',//HURRR DURRRR
               '89115065656 позвать Люду');
 
$regular='/^(8|\+7)((( |-|\(|\)|_|)*[0-9]( |-|\(|\)|_|)*){9})[0-9]$/';
$matches=preg_grep($regular,$numbers);
 
$regular='/\+7/';
$matches=preg_replace($regular,"8",$matches);
 
$regular='/-|_|\)|\(| |  /';
$matches=preg_replace($regular,"",$matches);
print_r($matches);
?>

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