https://stackoverflow.com/questions/29637142/raspberrypi-making-sip-outbound-calls-using-linphonec-or-an-alternative-sip-sof https://www.voip-info.org/asterisk-phone-linphone/
https://hardfault.life/p/telco-1 https://hardfault.life/p/telco-2
Turn handle to connect with voice controlled switchboard - Which extension do you require? emulate correct phone tones?
Rotary, Handle, button push