A callback is triggered before annotation is deleted. It is similar to the after deleation callback.

<?php
function my_component_init(){
		ossn_register_callback('annotation', 'before:delete', 'my_component_cb');
}
function my_component_cb($callback, $type, $params){
		//$params['annotation'] contains the annotation instance
}

Becareful as after deltation you may not able to access this annotation.