[from-external]
;BLOCK UNKNOWN NUMBER
exten => _X.,1,GotoIf($["${CALLERID(num)}" = "asterisk"]?BlockUnknown)

;BLOCK BY ANI
exten => _X.,n,GotoIf($["${CALLERID(num)}" = "123123123"]?BlockByANI)

exten => _X.,n(BlockUnknown),Wait(1)
exten => _X.,n,Playback(custom/blockUnknown)
exten => _X.,n,Wait(2)
exten => _X.,n,Hangup()

exten => _X.,n(BlockByANI),Wait(1)
exten => _X.,n,Hangup()