I am currently looking for a way to connect an intercom to the raspberry pi, at the moment, the intercom wires are connected to a regular telefphone ( only two wires needed ), when someone dials the phone rings, when I pick up I can talk to them and in order to open the door I keep the 0 button pressed. The phone has a switch for Pulse / Tone and only the Pulse mode actually does something.

Is there a way in which I can capture the call into the raspberry PI and eventually send back a Pulse in order to open the door?

I saw this question How can I generate frequency / pulse signals? but I don't think it's the same thing.

Another approach I am considering is to open the phone and somehow connect only the controls to it in order to prevent any power surges or a much higher voltage. Is that possible?

In the end I wish to connect this to a web server and send a push notification to my phone whenever someone calls and be able to open the door remotely.

Thanks a lot!