Hi Pythonpoole and thanks for your time.
I have been in contact with the provider (PennyTel) and one of their guys said they have tested with an SPA942 and the hold function works fine. So, I took one of my SPA942 units and reconfigured it and my firewall so that it is the only thing talking to PennyTel and it works correctly. I can make / receive calls and put them on hold and successfully resume the calls. However, I noticed that although I forgot to change the MOH Server setting in the SPA942 (which remains pointing to the MOH extension number in Axon) the MOH message is now coming from PennyTel instead of Axon, which intrigued me (as I was expecting no MOH at all since the SPA942 is no longer registered with Axon).
So, I reconfigured the firewall and SPA942 back to Axon. This time I removed the MOH server entry in the SPA942 configuration and tested calling again. Guess what ? Without the MOH server setting, I can now successfully put calls on hold and retrieve them !
Now here's the mystery, I have access to two other VoIP provider accounts. Using either of these other two providers in Axon, call hold and resumes work fine even with the MOH server setting in the SPA942. But with the PennyTel service, call hold and resumes won't work if I enable the MOH setting in the SPA942.
The million dollar question is -- why ??? Isn't the MOH function internal to Axon ? If it is, why does it work with 2 other providers by not with PennyTel ?