I have similar problem and reported by one of my friend who is using vonage.
#1. obi200
#2. A month back I ported my number to google voice and using without any issues.
I have verified all these options mentioned here but no luck. I am able to see that in google voice call history and but never rings on my obihai(handset). it is intermittent for that particular caller.
I am using obihai more than a month, except this issue it is really cool.