Here is an example subscribe method that you could place in a controller:
public function newsletter_subscribe() {
$this->auto_render = FALSE;
$post = $this->input->post();
if(!empty($post['newsletter_email'])) {
$email = $post['newsletter_email'];
$contactAdd = new IContact();
$result = $contactAdd->subscribeContactToList(array(
'firstName' => empty($post['newsletter_first_name']) ? '' : $post['newsletter_first_name'],
'lastName' => empty($post['newsletter_last_name']) ? '' : $post['newsletter_last_name'],
'email' => $email
), Kohana::config('ascension.newsletter_list_name'));
if ($result) {
echo "subscribed";
} else {
echo "error";
}
Session::instance()->set('subscribed', 'true');
} else {
echo "fail";
}
}