My IAX clients (checked with DIAX and idefisk) could not sent dtmf signals to the remote server. My iax.conf looks like this:
[general]
bindport = 4569 ; Port to bind to (IAX is 4569)
externip = mypublicip
localnet = 192.168.1.0/255.255.255.0
bindaddr = 0.0.0.0 ; Address to bind to (all addresses on machine)
delayreject = yes
disallow=all
allow=g729
allow=ilbc
allow=ulaw
allow=alaw
allow=gsm
allow=g723
jitterbuffer=yes
mailboxdetail=yes
#include iax_additional.conf
#include iax_custom.conf
#include additional_a2billing_sip.conf