This is what the original panel telephone looked like when we moved in.

Behind the phone is a mass of wires.

The back of the telephone looks equally complex.

This is as much of the phone as I have figured out so far.

I plugged the hole with a custom shaped block of wallboard and some spackling. I left the button that used to unlock the front door for visitors.

Spackling was too thick to smooth out, but joint compound was like pudding and made smoothing much easier.

All patched up and ready for paint.

I tried painting just the patch, but as good as paint matching technology is, it just doesn't match exactly. So the next day, I taped everything off so I could paint the whole wall.

Painting the whole kitchen wall.

All done. I can still see some rough areas, but we'll enjoy the finished wall for a bit.

Jim, here is a circuit diagram for the 1750 telephone I got from PDF file 502-706. It may help with the next steps.

I found some instructions online for converting an old phone into a wireless by taking apart a wireless handset and tying it into the mechanical parts of the vintage phone.

This is one of our extra handsets that I've taken apart to test with the wall phone.