I did have SIP ALG disabled.
This is what support said concerning SIP ALG, as related to my problem.
If you are using GV, the protocol is not SIP, hence disabling SIP ALG on the router, while it is always a good thing to do, does not explain the call cut-off.
- Obihai Support Team
I am going to reset the DLink to factory defaults and try it again to see if the problem goes away. I will be sure and report the results.
I did have to make some changes to it when I installed my NetTalk Duo a couple months ago, maybe those changes are causing the problem.