In index.php file after require_once($vqmod->modCheck(DIR_SYSTEM . 'library/cart.php'));
add:
require_once($vqmod->modCheck(DIR_SYSTEM . 'library/sms.php'));
Afer $registry->set('cart', new Cart($registry));
add
//Sms library
$registry->set('sms', new Sms($registry)); //where Sms is your class name
Once these changes are done you can call the class functions like $this->sms->getSmsInfo();
Have a nice day !!