At this point I'm willing to say this is a Telo problem . It works fine for a while (could be weeks), then a call comes in and after it ends, by either hanging up or leaving a VM on the home system, the analog side of the Telo stops functioning. The flower shows "blue" as in normal operations, the Telo network interface responds to ICMP ping, and the Telo shows as "online" on the Ooma web site. I can even use the Telo to listen to a VM that was left. Outgoing calls from the house just fail. Incoming calls go to Ooma VM. Coincidently, whatever is happening to the analog phone line is also leaving my ADT alarm panel in a state where it's trying to communicate via its download protocol too. While that may be of diagnostic value, it isn't causative, and rebooting the Telo puts the ADT system back into normal operation.
Nothing else to do but wait for Ooma to fix this. At least my ADT system, monitoring the phone line, sees the failure so I'm notified of it immediately via it's cell connection (which leaves VM with Ooma that alerts me the failure has happened), and I can then power cycle the Telo to restore it before anyone else in the house finds out and criticizes my choice to move to Ooma.
Here are dates of failures since last post. Fix is to power cycle the Telo.
Jun 5, 12, 25
Jul 16, 18.