Well, here's the promised explanation...

I had UVerse scheduled for installation today. Late yesterday afternoon AT&T must have done some work on the Network Interface box outside my house. Despite a label inside which clearly said not to connect to the home wiring, it appears that the wires for lines 1 and 2 were connected in some fashion. Since I feed my ATA output to my home wiring I suspect this resulted in the "dead air" behavior. Late last night I started debugging and found all was well with a phone directly connected to the ATA. And, unplugging all the phones and still connecting to the home wiring caused the issue - when it was light this morning I opened the NI box and saw what they had done.

Anyway, I talked to Cody a couple of times (thanks again) from work yesterday afternoon when I first encountered the issue and he did his best to help by tweaking at his end. But given what was happening, I realize that no amount of tweaking would have helped. Cody if you're reading it, it may be best to restore the setting to what they were previously - as I mentioned when I talked to you VOIPo has been flawless until this issue (which was clearly one not of VOIPo's creation). And, thanks for the time you spent on this.