One more update in this never ending series of frustrations. I also want to post this before moving on to a
new firmware in case the issues just disappear ... or god forbid get worse.
In summary, it's still not fixed, but evidence is pointing to the two CellCentric SPs interfere with each other, in some as yet unexplained manner.
The details: I formally reported the issue to Obi Customer Support. Getting a direct answer, or even a response after multiple mails has been a challenge, which of course adds to the frustration. Support replied with the usual: try **0 Option 27 (100 Mp full duplex), then connect the Obi directly to my Cable Modem (no can do for days at a time in my case) and then 'try a new router'. My response to this last was "I just spent $150 on a new SOHO router four weeks ago, do I really need to try a third one?"
After some back and forth messages, many of which went unanswered and then some more prodding, they replied to change the registration periods for the two CC SPs to 600 and 615 seconds. I tried that, but it was in vain, I believe, because on the System Status page for the two CC SPs it would show expires in XX seconds, where XX was never more than 60. They did not acknowledge this in an email response (to the original 'try 600 and 615' reply), but since I was at wits end I deduced to try 59 seconds and 60 seconds, with the intent to change to 53 and 59 seconds (the greatest prime numbers less than 60) the next time I purposely reboot.
The change to 59 and 60 seconds are correctly reflected in the CC SPs on the main status page, and the conclusion here is there's a 60 second maximum registration period (for CC or all SIP providers? Nothing I could fin din the admin manual). Even more encouraging, the change to 59 seconds and 60 seems to have 'reduced' the problem, but not completely eliminate it in my uptime test so far.
After six days of uptime, I had one episode with no dial tone and unresponsive via the
192.168.xxx.yyy Obi WebPage. After about a minute or two got dial tone back, and the
192.168.xxx.yyy started to respond. Unlike past episodes, this one did not result in a spontaneous mystery reboot, and uptime is now at 8 days, which is a new record. So those two points are progress (although small), in my experience.
In addition to the change to 53 and 59 seconds, (after I see how far I can go with the uptime using 59 and 60), I think I'll add two backup DNS servers,
Google Public DNS, which I think will be used in priority order ahead of my ISP's (Comcast) dynamically assigned DNS servers, based on the way I read the Admin Manual.