How to implement telephony?

Question

Telephony

Good day!
Faced a question on raising telephony. The task is as follows:

I will describe how I see it, I would like to get the correct terminology, diagram, manuals and so on from you.

There is a gateway (actually not, tell me) for 10 SIM cards. When calling to one of the sims, the call is sent to the -> server, then sent via the Internet to the client (linphone, etc.) to the mobile phone, tell which gateway to choose. Well, it is desirable to disassemble in stages. Asterisk server, right? Is it VoIP or SIP? Thank you!