iax.conf с сервера new_test:
[general]
bindport=4569
autokill=yes
disallow=all
allow=ulaw
jitterbuffer=yes
maxjitterbuffer=500
delayreject=yes
iaxthreads=15
iaxmaxthreads=50

register => new_test@192.168.0.79

[old_stable]
type=friend
qualify=yes
host=dynamic
nat=yes
auth=md5
trunk=yes
username=old_stable
secret=old_stable
insecure=invite,port;Стоит от безысходности
context=DLPN_WorkDialPlan
deny=0.0.0.0/0.0.0.0
permit=192.168.1.79/255.255.255.255


А так пишу в диалплане:
exten => _20XX,1,NoOp()
exten => _20XX,n,Dial(IAX2/new_test:new_test@192.168.1.79/${EXTEN},60,tT)
exten => _20XX,n,Hangup





Такие настройки на втором сервере old_stable: iax.conf:
[general]
bindport=4569
autokill=yes
disallow=all
allow=ulaw
jitterbuffer=yes
delayreject=yes
iaxthreads=15
iaxmaxthreads=50

register => old_stable:old_stable@192.168.0.102

[new_test]
type=friend
qualify=yes
host=dynamic
trunk=yes
nat=yes
auth=md5
username=new_test
password=new_test
insecure=invite,port;Стоит от безысходности
context=Dial_outgoing_local
deny=0.0.0.0/0.0.0.0
permit=192.168.0.102/255.255.255.255

extensions.conf:
exten => _104X,1,NoOp
exten => _104X,n,Dial(IAX2/old_stable:old_stable@192.168.0.102/${EXTEN},60,tT)
exten => _104X,n,Hangup