SIP hybrid server behind pfSense and setting up remote phone over openvpn - NAT

[mentalhemroids]

I posted this originally under NAT, but have had no feedback, so I'm hoping someone reads this area and has some ideas.

I wanted to figure out what is the best way to setup a sip phone remotely and I talked to a friend of mine that said I should look into NAT as my possible problem for audio problem.
I have a hybrid(meaning sip internally and out using standard lines) sip phone system internally that I thought I could use openvpn to setup a phone to work offsite.  I figured it would be better to use openvpn to make the connection secure and not open up the firewall for the sip server to be opened up for access.  I was able to get audio from the remote phone to cell or phone in the building, but no audio back to the remote phone.  I've looked at siproxy and wondered if that would even work for our setup.  Hopefully someone can steer me the right direction.

Thanks in advance.