why would renewing the lease on the WAN side IP address, where the address does not change, affect VoIPo? I don't see the logic.

Thanks for the suggestions, but I do have outgoing calls OK, incoming roll to the failover. Power-cycle the ATA (not the router) at VoIPo's suggestion, the problem goes away TEMPORARILY.

I don't have any custom settings like distinctive ringing, simultaneous ring.

VOIPo MUST alert CUSTOMERS by email, voice mail, robo-call to the failover number or by SOME MEANS, so the customer can know that incoming calls have been pushed to the failover number. I say this because it is THEIR EQUIPMENT (service) that elects to do so, and since outgoing calls are OK, the customer doesn't know.