Interestingly tones were audible on inbound and internal calls, however, this means that IVR’s are completely non-navigable.

The problem turned out to be due to the fact that it appears DTMF traffic was being sent out over a separate UDP port to the rest of the IAX traffic….calls sounded fine, but DTMF traffic was being blocked due to it running on port 4571.  We’ve opened the range 4569-4571 and now all is working fine….

The solution was to edit the the /tftpboot/sip.cfg and look for the line that says:

<digitmap dialplan.digitmap=”[2-9]11|0T|011xxx.T|[0-1][2-9]xxxxxxxxx|[2-9]xxxxxxxxx|[2-9]xxxT” dialplan.digitmap.timeOut=”3|3|3|3|3|3″/>

and replace with the correct number of digits for calls in your country…

<digitmap dialplan.digitmap=”[2-9]11|0T|011xxx.T|[0-1][2-9]xxxxxxxxxxx|[2-9]xxxxxxxxxxx|[2-9]xxxT” dialplan.digitmap.timeOut=”3|3|3|3|3|3″/>

You then need to restart the handsets in order for this to work.