Hi EdwardC,
I'm guessing you have a public static IP but am also curious as to which model of cable modem you are using. Are we talking an SMC, Motorola, or what?
QoS is a good thing to try. In most forum members' experience here, SIP ALG has
not been helpful and actually caused more problems in some cases.
Can you try to place your OBI in the DMZ of your Netgear 338 Router? I feel this would be your best option to test. As this would expose the OBI to the internet/WAN side, just make sure that you have a good password in place on the OBI. Since you said you cannot connect the OBI directly to your cable modem, the
DMZ option is what I would try next.
Quality issues could be related to GV, and they could also be related to your network (internet) route. Even with a very high-speed internet package, there are other issues such as latency that can affect real-time communications. Cable internet providers are 'typically' notorious for latency problems. This of course depends on the route of your traffic (source and destination). So, yes, it could be something else, and it could be GV, but if it was your internet connection or GV, I would expect to see poor quality issues and not complete-disconnects 50% of the time. If you could test with another VoIP provider, like Callcentric, that would help in the troubleshooting process.
Just my two cents,
pc44