in extensions

[fwd-trunks]
exten => _393.,1,SetCallerId,(<431505>)
exten => _393.,2,Dial(IAX2/$431505:$william@iax2.fwdnet.net/${EXTEN:1},60,r)
exten => _393.,3,Congestion

[fromiaxfwd]
exten => 431505,1,Goto(local-access,200,1)
exten => 431505,2,Hangup

in iax

[iaxfwd]
type=user
context=fromiaxfwd
;auth=rsa
;inkeys=freeworlddialup
deny=0.0.0.0/0.0.0.0
permit=65.39.205.0/255.255.255.0