How to implement POST request in custom services module?
In order to change into the POST request. You just change the source of resource from path to data. For example:

function module_rest_services_resources() {
  return array(
  'new_note' =&gt; array(
     'actions' =&gt; array(
       'retrieve' =&gt; array(
         'help' =&gt; 'Retrieves a note',
         'file' =&gt; array('file' =&gt; 'inc', 'module' =&gt; 'module_rest'),
         'callback' =&gt; '_module_rest_retrieve',
         'access callback' =&gt; '_module_rest_access',
         'access arguments' =&gt; array('view'),
         'access arguments append' =&gt; TRUE,
         'args' =&gt; array(
           array(
             'name' =&gt; 'id',
             'type' =&gt; 'int',
             'description' =&gt; 'The id of the note to get',
             'source' =&gt; array('data' =&gt; 'id'),
             'optional' =&gt; FALSE,
            ),
          ),
        ),
      ),
    ),
  );
}