I guess what I am not understanding here is why we aren’t seeing the audio from the grandstream in your RTP debug.
The RTP debug should show two way audio
received from public ip
sent to private ip
received from private ip
sent to public ip
right now we are only seeing 1/2 the story. can you enable both “rtp debug” and “sip set debug” and send me the entire transaction which should be 2 INVITE (in/out) ending at the BYE/OK.
ok, that looks better. it does appear that asterisk is receiving the RFC2833 packet and forwarding it out. Your configuration is all correct and the phone is functioning properly and asterisk appears to be functioning properly.
There is one other thing you should try before pointing the finger at your ITSP and saying they aren’t dealing with the DTMF properly. I would suggest upgrading to the most recent version of 1.4 (1.4.24.1 as of today) to see if the problem goes away.
If that doesn’t fix things then it’s time to call your ITSP to see what they say.