Or a cleaner way.....

In iax.conf :

[iaxRpt](!)
type=friend
host=dynamic
disallow=all
allow=ulaw
allow=gsm
allow=g726aal2
codecpriority=host
requirecalltoken=no
jbenable=yes

[node_A](iaxRpt)
secret=foo_bar
context=radio-gui_1

[node_B](iaxRpt)
secret=bar_foo
context=radio-gui_2



In extensions.conf :

[radio-gui_1]
exten => 27783,1,rpt(27783|X)
[radio-gui_2]
exten => 27826,1,rpt(27826|X