Self-hosted VoIP? - eviltoast

I would like to use a SIM7600X 4G Expansion Board (like this one) to connect my raspberry pi to the mobile network.

In this raspberry pi I am also running an XMPP server.

I want to then create an account that will bridge SMS messages between the SIM7600 and my XMPP account (should be easy), and ideally it should also be able to bridge phone calls (might be difficult?).

I know about the XMPP-VoIP JMP.chat, and since they are open source I can get some inspiration from them.

I will try to implement something myself, but I am not an amazing programmer. So I am wondering whether there is already some open source project that is more tailored for this application.