@djohnson
This is a late reply but it may assist someone else in future.
The VOIP audio traffic (RTP) require separate UDP ports to be open. The exact range will vary depending on your VoIP system.

Hence, if the RTP ports are not open, you can experience a "working" system, but with a complete lack of audio.

Thanks, I will look into setting up OpenVPN instead.

I could not find my previous post, I thought it was not posted properly, now I found it but can not remove this one... please Admin, remove it and pardon my mistake