I have experienced the same issue. My friend has an Obi202 setup with a GV number and I have an Obi202 with a GV number. Until sometime yesterday we were able to call each other with no problems. Now, when we try to call each other, the phone will ring, but when the other person picks up we are unable to talk to each other. It appears that the call has connected, but you can't hear the other person. Tried updating both boxes to the latest firmware, but it didn't help.
To troubleshoot, I tried calling from my Obi GV number to another GV number that forwards to my cell phone. Same issue. Call rings and appear to connect, but you can't hear anything.
Next, I tried taking Obi out of the equation. I tried initiating a call from Gchat to another GV number that forwards to my cell phone. The same thing happened. The call rings, but when I answer I can't hear anything from the other line.
It seems to be something Google has done that you can't call from one GV number to another GV number any longer, at least in Gchat/forwarding mode. I don't know if this is a mistake or if they did this on purpose because they think you should be able to do this in Hangouts now.
I guess the solution for me and my friend is just to call each other's Obi box directly rather than doing it through GV, which works fine i suppose. But it is unfortunate that if someone tries calling my Obi GV number from a GV number, or if I try to call their GV number, it just isn't going to work unless Google decides to fix this.