Quick two files to have Zendesk post to zendesk.php on a trigger, which will then ask Twilio to go to twilio.php and do stuff. Like call you and text you. You will need to load the Twilio PHP helper.

twilio.php

<?php
	include 'Twilio.class.php';
	$subject = urldecode($_GET['subject']);

	$response = new Services_Twilio_Twiml();
	$response->say('Hello.  New Zen desk ticket.');
	$response->pause("");
	$response->say($subject);
	$response->sms(
		'New support ticket: ' . $subject,
		array(
			'to' => '+1231231231', // Your number to SMS to..
			'from' => '+112312312' // Your Twilio number.
		));
	
	print $response;

?>

zendesk.php

<?php
	if (!isset($_POST['some-string-here'])) // This string you'll set in Zen Desk as the 'attribute name'.
	{
		exit('You are not Zen Desk.  Get off mah lawn!');
	}
	else
	{
		$subject = urlencode($_POST['some-string-here']); // Update that same string here as well.
		$subject = htmlentities($subject);
		$twixml = 'http://sajanp.com/twilio/twilio.php?subject=' . $subject; // Update the URL to your twilio.php file here.
	}
	
     	include 'Twilio.class.php';

        $sid = "XXXXX"; // Your Twilio sid.
        $token = "XXXXXX"; // Your Twilio token key.

        $client = new Services_Twilio($sid, $token);
        $call = $client->account->calls->create
        (
        	'XXXX', // Your Twilio number.
                'XXXX', // Your number to call.
                $twixml
        );
?>