@Silversam: Thanks!

@RotaryDialTommy:
This project is indeed not something a sane person would do,
it was more a learning experience and something I'd wanted to do for a while.
Cost wise, it's probably not cheaper than a 551a on ebay, but it is lighter, lol

@DimensionSeven:
Your wifi idea sounds neat. I'd actually thought about using
1a2 over wifi, but I wasn't familiar with digital to analog for voice
when it came to converting two wire to four wire. So I held back
on that project, as it took me too far into D/A, A/D telephony.
I might try that as a follow up project, though!

Of interest for 1A2, there are cell phone bridges that can connect
cell phones to POTS, and therefore 1A2. I looked into that a few
weeks ago, the box is around $100. Was curious to experiment with that.
The reviews on Amazon for the product were mixed, but promising.

One 1a2 feature I regret I didn't want to get into is an auto attendant
and voice mail, two features that have been important for my business.
Having an auto attendant feature gets rid of robocalls! I have an AT&T
1080 system with that feature, and love it just for squashing the 4 or 5
junk calls per day my business lines get.

@Arthur:
Regarding ComKey 416: yes! Some ComKey 416 features
inspired me for this project, esp DSS and intercom.

One of my folks worked at an office where they had a 416 system,
and I was familiar with its operation by talking to the head
secretary; she knew all the features, and showed me on her
primary set, which I remember was a great deal larger than the other sets.
So I was familiar with how it worked.

Later they ripped out the 416 system (early 80's), switching to
a "horizon" system, IIRC. (I recall it had a different ring, and
maybe fancier buttons?) Again, the same secretary showed me the new
system. She had noticed my interest in the phones, and thought
to rescue a 416 satellite set from being tossed out, which I still have.
Has a rotary dial. So as a young teen I studied that quite a bit.
I have a drawing I made of it on my ComKey 416 page:
[Linked Image from seriss.com]

Great modular design internally. Never had or found repair schematics
for ComKey phones, though, so there's a lot I don't know about their
internals. I also never got around to opening my primary set, hrm. Don't know
if I should be scared to look or not.

Some years ago I purchased a touchtone satellite 416 set, pic of it here.
..and later, bought a primary set off ebay. That was great, because
then I could actually get it all working as intended.

At the time access to ComKey documentation even on the net was limited,
but was able to find some hookup docs, and reduced it to a single document
I also posted on my ComKey 416 page.

Re: C*NET, nice; thanks for the link, and the offer to discuss stuff.
Indeed I don't find myself on the east coast much anymore; used to
live there. Not missin the cold!