I recently updated the Clickatell PHP Library with added support for MT callbacks (tag 1.0.1). In order to utilize it, you can register a closure callback with the Clickatell library using Clickatell::parseCallback();.

 1 <?php
 2 
 3 use Clickatell\Clickatell;
 4 
 5 Clickatell::parseCallback(function ($values) {
 6 
 7     // Executes if it finds the required parameters in $_GET
 8     // apiMsgId, cliMsgId, to, timestampe, from, status, charge
 9     var_dump($values);
10 
11 });

Future versions will hopefully include MO callback support.