My dad installed a Nutone 4406 unit in my parents house years ago.   It has the typical Nutone doorbell recessed in the brick.  The intercom system no longer works, can't get a new wire in.

My mom would like something that would replace the nutone doorbell, I would like her to have some form of video doorbell.  She has an iphone,  does Ring or Doorbird have some sort of "retrofit" kit?

Doorbird surface mount D101 is their retrofit model. Actually the one I have at my house.

In NE, a lot of the doorbells are installed between the doors and the glass sidelights. This was the only thing I could make work in its location.

It's ancient technology, but something from Aiphone might do for her.

The website is not at all helpful. You'll have to talk to someone at the factory, so don't start researching this on Saturday afternoon.

Go to a metal shop and get a piece of stainless cut to cover the hole. Mount new doorbell.

Get a Nutone plate from Kyles Switch Plates.
[Link: kyleswitchplates.com]
Mount doorbell to it and use the existing wire back to the main unit.
Replace the transformer in old Nutone unit to provide enough juice for the doorbell and either disconnect everything else in the main unit or there are diagrams online where you can add a relay and have it still ring through the Nutone.

[Link: doorbird.com]