I know this is a long shot, but here goes. We are installing a TDA50 in a residence which shares a Lee Dan PK543 apartment intercom system with 4 other tenants.
We are limited in our ability to change existing equipment/wiring. I am wondering if there is a creative way of incorporating the existing call station to work as a door phone on the TDA.
The home owner is hoping to greet visitors & release the door from system phones.

Any ideas would be much appreciated.
- Patrick L.