Retrofit / integration with building intercom system?

I’m looking for a way to integrate a building’s apartment intercom system with ST, preferably without changing the entire system. The building is setup with IR103E Tektone Apartment Intercom Station, 3-Wire. I believe there are 4 fundamental features required:

  1. Cause an alert/event in ST based on a contact closure. I know there is plenty of closure hardware out there, like a FortrezZ MIMOlite
  2. Close a circuit to trigger unlock the front gate. Again, the same FortrezZ MIMOlite can do this part.
  3. Encode an audio signal when someone is at the entrance trying to talk. I’m pretty sure this is a dumb analog signal so any encoder with a DTH would work… maybe even one of the supported video cameras in just audio-only-mode…?
  4. Return the audio signal when I talk into my phone (this is probably just #3 running in reverse so long as I can push an audio stream back to the device).

Let me casually ignore response times and latency for now. I’m just curious if I can basically create a Ring / Doorbird style setup, but (a) no need for video and (b) retrofitting onto a super old analog building infrastructure.