Looks good, but I want to physically connect the landline phone as an audio device too... that solution seems elusive. I could probably assemble a circuit to do

Looks good, but I want to physically connect the landline phone as an audio device too... that solution seems elusive. I could probably assemble a circuit to do it, though I'm not sure I could design one. I have this Linksys VOIP router that I used to use on my old landline to interface with an Asterisk server, but I don't think the firmware supports this use case.