public function setCustomerNo($pno, $custNo, $encoding = null)
    {
        //Get the PNO/SSN encoding constant.
        if ($encoding === null) {
            $encoding = $this->getPNOEncoding();
        }
        $this->_checkPNO($pno, $encoding);

        $this->_checkArgument($custNo, 'custNo');

        $digestSecret = self::digest(
            $this->colon($this->_eid, $pno, $custNo, $this->_secret)
        );
        $paramList = array(
            $pno,
            $custNo,
            $this->_eid,
            $digestSecret,
            $encoding
        );

        self::printDebug('set_customer_no', $paramList);

        $result = $this->xmlrpc_call('set_customer_no', $paramList);

        return ($result == 'ok');
    }