Steps:
1: get file content > base64
2: get session key
3: import survey
4: release session key

the code:

function importSurvey($SurveyID, $strFilename) {
global $DATABASE_SETTINGS;

    define( 'LS_USER', '****' );
    define( 'LS_PASSWORD', '****' );

//1: get file content
$file = ???->qn_filepath . $strFilename;

echo "<br>File exists:"; var_dump(file_exists($file));
if(!file_exists($file))
{
return "File not found @ ". $file;
}

    $hFile = fopen($file,"r");

    $data = fread($hFile, filesize($file));
    //var_dump($data);
    $data = base64_encode($data);
    //var_dump($data);
    fclose($hFile);

    if($data == null)
        return "Error reading file content: ". $file;

    // instantiate a new client 
    $rpcClient = new jsonRPCClient(?->rpcClient ."/limesurvey/index.php/admin/remotecontrol", $debug=true);

/2: get session key
$SessionKey = $rpcClient->get_session_key( LS_USER, LS_PASSWORD );

echo "<br>SessionKey: "; var_dump($SessionKey);
if($SessionKey == null)
return "Error getting ls session key: ". $SessionKey;

//3: import survey
$result = $rpcClient->import_survey($SessionKey, $data, "lss", null, $SurveyID);
print_rr($result);
if(is_array($result))
{//fail
$rpcClient->release_session_key( $SessionKey );
return $result->status;
}else{
$SurveyID = $result;

        $result = $rpcClient->activate_survey($SessionKey, $SurveyID);
        print_rr($result);
    }

//4: release session key
$rpcClient->release_session_key( $SessionKey );

    return $SurveyID;
}

//util funtions:
function print_rr($value)
{
echo "<PRE>";
print_r($value);
echo "</PRE>";
}