<sales_order_payment_cancel>
                <observers>
                    <Barcatsia_Smsntf_Model_Observer_cancelOrder>
                        <type>singleton</type>
                        <class>Barcatsia_Smsntf_Model_Observer</class>
                        <method>smsntf_cancel_order</method>
                    </Barcatsia_Smsntf_Model_Observer_cancelOrder>
                </observers>
           </sales_order_payment_cancel>

public function smsntf_cancel_order($observer){


        $order = $observer->getEvent()->getOrder();
        $orderIds = $order->getId();




        if(Mage::getStoreConfig

('testsection/cancel_order/Smsntf_module_activation')){

        $layout = Mage::app()->getLayout();


            $order     = Mage::getModel('sales/order')->load($orderIds);

        $message_for_send = Mage::getStoreConfig

('testsection/cancel_order/Smsntf_text_field_msg');
        $http_url = Mage::getStoreConfig

('testsection/cancel_order/Smsntf_text_field_api_calling_url');
        $arr_params = array('Smsntf_text_field_authkey', 'Smsntf_text_field_mobile',

'Smsntf_text_field_senderid', 'Smsntf_text_field_routeid', 'Smsntf_text_field_additional',

'Smsntf_text_field_additional', 'Smsntf_text_field_additional1',

'Smsntf_text_field_additional2', 'Smsntf_text_field_additional3',

'Smsntf_text_field_additional4');

        //replaceing %O% with Order Number
        $message_for_send = str_replace('%O%',100000000+intval($orderIds[0]),

$message_for_send);

        //replaceing %N% with Mobile Number
        $message_for_send = str_replace('%N%',$order->getdata

('customer_firstname'),$message_for_send);

        //replaceing %A% with Grand Total
        $message_for_send = str_replace('%A%',$order->getdata('grand_total'),

$message_for_send);

        $http_url .='?'. Mage::getStoreConfig

('testsection/cancel_order/Smsntf_text_field_Msg_prm').'='.urlencode($message_for_send);
        for($a=0; $a<sizeof($arr_params); $a++){
            if(trim(Mage::getStoreConfig('testsection/cancel_order/'.

$arr_params[$a]))!=''){
                if(trim($arr_params[$a])!='Smsntf_text_field_mobile')
                    $http_url .= '&'.Mage::getStoreConfig

('testsection/cancel_order/'.$arr_params[$a]);
                else
                    $http_url .= '&'.Mage::getStoreConfig

('testsection/cancel_order/'.$arr_params[$a]).'='.$order->getBillingAddress()->getData

('telephone');
            }
        }

        //printing system->configuration inputs value
        //      echo Mage::getStoreConfig

('testsection/cancel_order/active');
                $this->send_sms($http_url);

        }else{
            return false;
        }
    }

$payment = $observer->getEvent()->getPayment();
$order = $payment->getOrder();