Ha ha about the wife joke.
I hesitate to offer any advice on this, since there are national and state building codes and laws involved with elevator safety requirements. If this is a private home with a private elevator, you may be exempt, but I just wanted to put that disclaimer out there.
Don't use Google Voice for this solution. It cannot make 911 emergency calls.
The bigger picture is: yes, the OBi is an analog telephone adapter, that connects to a standard analog telephone or telephones to make and answer calls. Yes, you can, in theory, hook it up to your home's telephone wiring, if you first make darn sure that the telephone company's external connection is disconnected at the point of demarcation (the box on the outside of the house or in some place like a basement, garage, etc.).
Also: Obihai advertises using the product with alarm panels, but it is highly unreliable for this purpose, due to the very old and primitive communications method used by alarm panel dialers.
If you actually want to use the OBi for a landline replacement, you'd need to subscribe to service from an internet telephone service provider (SIP ITSP), such as
voip.ms or Callcentric, on a per-minute basis for minimal use. The monthly cost would be around $2. Those ITSPs provide E911 service.
Alarm companies have mostly moved to monitoring/communicating via a cellular/LTE communicator, often with a dedicated internet connection for backup. That's how mine works now. Both the alarm panel and the mobile radio have backup batteries.
And, with regard to the need for an analog telephone, surely a friend or relative has one you can borrow temporarily. If not, you can buy a basic analog phone at any big-box store or Amazon for perhaps $10-15. Example:
https://www.amazon.com/dp/B01GA7JR8C