Using Asterisk as a H.323 gatekeeper


I had already a H.323 configuration with GnuGK

I need to configurer a voice message response when user dial an unregistered phone number

It seems that GnuGK does not act as an announcement server and needs to use Asterisk to do that

What is the best method to configure Asterisk to make voice announce when user dial bad number from H.323 ipphone ?

Is it possible to use only asterisk ( with chan_h323 , or chan_oH323 , or chan ooH323) ?