wp meta_query meta_value compare =REGEXP delimited by space

by

solution for this question is :

taking the example above 75213332 bla bla bla bla ..
to search for all post that have the custom_tel 75213332 the REGEXP will be ^(75213332) so in this case 

array(
  'key' => 'custom_tel',
  'value' =>'^('.$tel.')',
  'compare' => 'REGEXP'
  )