How to automate an/this intercom?

I have the following intercom:

Unfortunately there is no brand/type/what-so-ever. However, it seems to be very simple: There are 4 wires coming out of the wall (white, green, red, black) out of which only two are used (green and white) which go into P1.

The door can be unlocked with the Unlock/Key button which simply connects the metal bridge SW1.

For the handset, there are four wires yellow, green, black, red that connect the handset from P3 via a simple Western/RJ11 connector.

Finally, there is the big switch SW2 which connects voice to the headset. I would like to retro-fit this into a "smart intercom" (without cloud): It should connect to HomeAssistant/Asterisk and I’d want to be able to operate the Unlock functionality from phone. If possible, route voice to my phone if somebody rings.

1. Can this be a standardized system and do there exist simple, pre-made systems that can retrofit this intercom into a "smart" one?
2. I have heard people using an "OBI200" to connect their intercom to Asterisk. That would be perfect but I don’t know how to connect it. If I would only connect the RJ11 connector, how would I operate SW1 and SW2?
3. In the worst/simplest case I’d plan to use a Shelly 1 to operate SW1. Shelly needs power supply (>16V but takes <1W). Is this something I can take from the green/white or black/red wires or will this be an issue?