@GPz1100 and drgeoff: I intended to write a message thanking you both because the phone was working (registered) after restarting the router and Obi100, but SP1 is now back to offline.
I reset the router and Obi device again just now, which put me back to registered/solid green light and able to use the phone. But the Obi green light is now flashing and, sure enough, I'm again offline. All I get is a couple of minutes of connection.
The WAN IP address is dynamic and the numbers are completely different from my router IP. I don't know how often Charter/Spectrum changes the IP address, although it should be at least 24-48 hours; static IPs are for their business accounts, AFAIK, dynamic for home.
I should add that whatever the WAN IP has been, we never had a problem with calls until this morning when the end of OBi100 caught up with us.