So ... one station is inside a house or apartment, and one is outside pointed at the street beyond the porch, or down at the gate, or ...?

"The more I learn, the more I don't know."

The less you say, the more we don't know.

ak

 

...
"The more I learn, the more I don't know."
The less you say, the more we don't know.
ak

LOL, I wasn't being secrecy or anything. It's just how I like to do my very early research. I like to keep the it open at the early state, I ask questions like these so I can get lots of different answers from different people with different background, and from different perspectives.

From time to time, I will get something I have never ever thought of before. For me, that is fascinating, as it shows me to new ideas. (even the idea has nothing to do with my intended application)

However, I understand that it may be annoying for you, as you have so much knowledge about this and you can't give a tailored suggestion.

For now, the intended application is the station is in one room of a building, and there are multiple remote stations in different rooms. The main station needs to be able to talk to different remote stations in different rooms (only one at a time for now, 2 is better), duplex is preferred. HD voice is nice. And just like other projects, we want everything but also want it reasonably low cost, well, I think you get the idea

 

Another approach, I have here at home, SPA942 VOIP phones, and at the moment, an old Win7Pro laptop running as a telephone exchange.
The outside line interfaces with an SPA3102 ATA and rings the phones, and I can ring out too. Each phone can call the others, individually or in a group. And if I dial the other phone number, but add an 8 in front off the target numbed, the called phone gives a different ring tone, then becomes an on the hook speaker phone intercom. This is handy as I can call my wife in her sewing studio to ask if she wants a coffee. She can answer without getting up from her sewing.
My previous PABX was in an EEEbox, but the Raspberry Pi works well. But if you use a Pi, make the file system on the SD card read only. I had a Pi based PABX that dies after about 4 years with over use of the SD card. Or make a backup of the SD card, and take the original our and run on the copy. I made a backup but used the original. Then when the SD card failed, I put the backup in only to find it was just the boot partition backed up

There are also a number of small PABX boxes available if you do not want to roll your own.
The phones are POE so just have a central POE switch.
This is just another option that may be worth a look, although it is a bit complicated to set it up.