How to create a similar application?

Question

Python

There are programs like Linphone where you can enter a username, caller ID, password and server from any SIP operator and call using this program.
I need to make the same program, where you can read about it in general, how to connect with this sip operator to make calls, maybe there are some libraries, any info will be useful, tk. I don't even know how to google it, what it's called.
(Preferably in python)

Answer 1

SIP SIMPLE Client SDK
PJSUA Python Module