function theme_myModuleBox($title, $content, $region = 'main')
{
  $output = '<h1 class="title">' . $title . '</h1><div>' . $content . '</div>';
  return $output;
}

theme('theme_myModuleBox', $title, $content, $region = 'main');

/**
 * Implements hook_theme().
 */
function myModule_theme() {
  return array(
    'myModuleBox' => array(
      'arguments' => array(
        'title' => '',
        'content' => '',
        'region' => 'main',
      ),
    )
  );
}