Adding a Newsleter Signup of Other Module to Your Offline Page

1. Edit the file /templates/YOURTEMPLATE/ofline.php (or if that doesn't exist edit the file /templates/system/ofline.php

2. Add this code

<h2>Launching soon - please sign up for more information</h2>
<?php
    jimport("joomla.application.module.helper");
    jimport("joomla.plugin.helper");
    jimport('joomla.filesystem.folder');
    jimport('joomla.filesystem.file');

    $document = JFactory::getDocument();
    $renderer = $document->loadRenderer('module');
    $result = null;
    $modules = JModuleHelper::getModules("offline");
    foreach ($modules as $module) {
        $content = $renderer->render($module, array(), $result);
        echo $content;
    }
?>

3. Add your module to a custom module position called 'offline' and set it to display on all pages.