<?php
$inStr = 'Hey you guys';
$tokens = array();
for(explode(' ',$inStr) as $bigToken)) :
$tokens[] = $bigToken; //take care of individual words
$tokens = array_merge($tokens, str_split($bigToken)); //take care of single letters
for($i = 2; $i < strlen($bigToken); $i++) :
$tokens[] = pop(str_split($bigToken)); //only need the first element here.
endfor;
endfor;
print_r($tokens);