Custom applications can be called by Multi-Level IVR and can, in turn call the IVR manager. Above is a very simple example of a Custom App which has been called by the IVR Manager. It simply plays a holding message and hands control back to menu 0002 in the IVR system. While this example is trivial, the custom app has full control of the call and could have used any available mechanism or application (including its own user-written agi) in the asterisk system.