I have set up open VFX on Softfone X-Lite(3).
It rings out fine and speech can go both ways.
However when it is rung (from outside), it launches ok, rings ok, but when answered, speech only comes in but can't go out until "Hold" is pressed and released or "Line 2" is pressed and returned to Line 1 (where the call is).
Also it worked both ways fine with an I-Talk account.
There is no ATA box on line to confuse it and it is the same on two different computers.
Both computers are on a Rural Wireless Broadband Network (Scorch North Canterbury).
One Computer has a real-world IP address and the other one is Scorch "In-House" connected.
Some Super-Geek will probably know the answer to this right away !