iax.conf on  Server A

[general]
language=de
bindaddr=0.0.0.0
port=4569
disallow=all
allow=ulaw
allow=alaw
allow=gsm
tos=lowdelay
trunk=yes
jitterbuffer=no
forcejitterbuffer=no
tos=lowdelay
autokill=yes


[asterisk2]
type=friend
context=asterisk-in
host=192.168.0.219
secret=1234
-------------------------------------------
extensions.conf on server A

[general]
port = 5060
bindaddr = 0.0.0.0
context = sonstige

[asterisk-in]
exten => _12XX,1,Dial(SIP/${EXTEN}); interne Gespräche via Sip

[raus]
exten => _22XX,1,Dial(SIP/${EXTEN}) ; externe Gespräche anderer Asteisk intern
exten => _0X.,Goto(asterisk2,${EXTEN},1) ; externe Gespräche via anderer Asterisk

[asterisk2]
exten => _XX.,1,Dial(IAX2/asterisk1@asterisk2/${EXTEN})
---------------------------------------------------
IAX.conf on Server B

[general]
language=de
bindaddr=0.0.0.0
port=4569
disallow=all
allow=ulaw
allow=alaw
allow=gsm
tos=lowdelay
trunk=yes
jitterbuffer=no
forcejitterbuffer=no
tos=lowdelay
autokill=yes


[asterisk1]
type=friend
context=asterisk-in
host=192.168.0.204
secret=1234
--------------------------------
extensions.conf on Server B

[general]
port = 5060
bindaddr = 0.0.0.0
context = sonstige


[asterisk-in]
exten => _22XX,1,Dial(SIP/${EXTEN})
exten => _XXXX.,1,Goto(provider-out,${EXTEN},1)

[asterisk2]
exten => _XX.,1,Dial(IAX2/asterisk1@asterisk2/${EXTEN})[root@localhost ~]#