Sample code that shows how to send an SMS message using Twilio whenever a payment is posted to one of your FreshBooks invoices. Read the full tutorial here: http://www.twilio.com/blog/2011/06/how-to-create-sms-payment-notifications-for-freshbooks-using-tw

handle-payment.php

<?php
	// The Twilio helper library. Get a copy here: http://www.twilio.com/docs/libraries/
	require_once('twilio.php');

	// Uses the FreshBooks helper library written by Milan Rukavina. Get a copy
	// here: http://code.google.com/p/freshbooks-php-library/
	require_once('FreshBooks/Payment.php');
	require_once('FreshBooks/Invoice.php');
	require_once('FreshBooks/HttpClient.php');

	// FreshBooks account information
	$FreshBooksUrl = 'https://XXXXX.freshbooks.com/api/2.1/xml-in';
	$FreshBooksToken = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';

	// Twilio account information
	$AccountSid = 'ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';
	$AuthToken = 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX';
	$ApiVersion = '2010-04-01';

	// The phone number that appears as the caller ID when an SMS is received.
	// This must be a Twilio phone number.
	$From = '+1XXXXXXXXXX';

	// The phone number the SMS notification should be sent to.
	$To = '+1XXXXXXXXXX';

	$client = FreshBooks_HttpClient::init($FreshBooksUrl, $FreshBooksToken);

	// Sent by FreshBoooks the first time a webhook is added in order to ensure
	// that the user is the owner of the callback script being registered.
	if ($_POST['name'] == 'callback.verify')
	{
		$response = '<request method="callback.verify"><callback><callback_id>'.$_POST['object_id'].'</callback_id><verifier>'.$_POST['verifier'].'</verifier></callback></request>';

		$client->send($response);

		exit;
	}

	// FreshBooks has sent us a notification that a payment has been posted to an invoice.
	$paymentId = $_POST['object_id'];

	$payment = new FreshBooks_Payment();
	$invoice = new FreshBooks_Invoice();

	$payment->get($paymentId);
	$invoice->get($payment->invoiceId);

	$message = "You just got a payment of {$payment->amount} from {$invoice->firstName} {$invoice->lastName} ({$invoice->linkView})";

	$twilio = new TwilioRestClient($AccountSid, $AuthToken);

	// Send the SMS notification using Twilio
	$response = $twilio->request("/$ApiVersion/Accounts/$AccountSid/SMS/Messages", 
		"POST", array(
		"From" => $From,
		"To" => $To,
		"Body" => $message
	));

	if ($response->IsError)
	{
		echo "Error: {$response->ErrorMessage}";
	}
	else {
		echo "Sent notification";
	}
?>