ajaxifying simplenews subscribe is there a way to ajaxify simplenews subscribe to newsletter block?
I was thinking of hook_form_alter ing it and adding my ajax callback, But its not working.

my_module_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if ($form_id === 'simplenews_block_form_7182') {
    $ajax = array(
          'callback' => 'simplenews_block_form_validate',
          'wrapper' => 'simplenews_wrapper_block',
          'method' => 'replace',
          'effect' => 'fade',
          'progress' => array('message' => '')
        );
    $form['submit']['#executes_submit_callback'] = TRUE;
    $form['submit']['#ajax'] = $ajax;


but now when I trigger the submit button i get 
Fatal error:  Call to undefined function simplenews_block_form_validate() in /includes/form.inc on line 1460
Hope this will help you,

In Drupal 7, you can achieve this using form_load_include OR require_once 

Try form_load_include() OR require_once() in your form alter.

function test_form_alter(&amp;$form, &amp;$form_state, $form_id) {
 switch ($form_id) {
    case 'simplenews_block_form_ID'://add your form_id
        require_once(DRUPAL_ROOT . "/modules/contrib/simplenews/includes/simplenews.subscription"); 
        //OR
        form_load_include($form_state, 'inc', 'simplenews', 'includes/simplenews.subscription');
    break;
   } 
}


Reference