Fatal error: Call to a member function getTelephone() on a non-object in  model/Observer.php on line 125

public function salesOrderPlace(Varien_Event_Observer $observer)
{
try{
        Mage::log("New Order Placed");


        $order = Mage::getModel('sales/order');

        $incrementId = Mage::getSingleton('checkout/session')->getLastOrderId();
        Mage::log("Order ID:".$incrementId);

        $order = Mage::getModel('sales/order')->loadByIncrementId($incrementId);

        if ($order instanceof Mage_Sales_Model_Order)
        {
          if($this->getHelper()->issalesOrderPlace())
          {

            $mobilenumbers = $order->getBillingAddress()->getTelephone();

            $message = $this->getHelper()->getOrderMessage($order); //enter Your Message
            $customerName = $order->getCustomerName();
            //curlApicall : this method will return tru or fale.
            $retunValue = $this->getHelper()->curlApiCall($message,$mobilenumbers,$customerName,"New Order");

          }
          if($this->getHelper()->issalesOrderPlaceForAdmin())
          {
            $mobilenumbers = $this->getHelper()->getAdminMobileNumber();
            $message = $this->getHelper()->getOrderMessageForAdmin($order); //enter Your Message
            $customerName = $order->getCustomerName();
            //curlApicall : this method will return tru or fale.
            $retunValue = $this->getHelper()->curlApiCall($message,$mobilenumbers,$customerName,"New Order");

          }
        }

    //return false;
  }catch(Exception $e) {
         Mage::log($e->getMessage());
  }
}