Simple. Call Hangup without having called Answer. Even dropping off the end of the dialplan will do this. (For ISDN, you may need to enable out of band signalling…
The NOOP dialplan and, in fact, no dialplan at all, will hangup immediately, without answering the call.
Note that I did suggest you look into this option, as it might be that the service provider assumes an early media indication is a chargeable event:
; PRI Out of band indications.
; Enable this to report Busy and Congestion on a PRI using out-of-band
; notification. Inband indication, as used by Asterisk doesn't seem to work
; with all telcos.
;
; outofband: Signal Busy/Congestion out of band with RELEASE/DISCONNECT
; inband: Signal Busy/Congestion using in-band tones (default)
;
; priindication cannot be changed on a reload.
;
Maybe your service provider is aware of what you are doing and has added some special rules for you, as I almost commented in the first place that this might be considered a fair usage breach. You are getting a service without covering the cost of that service.
can i detect the DID on which the call is coming and write a plan to hangup directly
How do missed call campaign operate, lot of vendors provide missed call campaigns how they do that in a asterisk machine