A phone number is a phone number. You don’t “create” one, you lease/subscribe to a carrier that did the work to become an authorized phone carrier in a specific country.

If your question is “how do I start my own carrier in my country ?”`, first step would be going to the government body that oversees telecom operations. Usually, you’d need to complete administratives and technical requirements, such as :

• getting an operator license
• implementing a technical solution to bill your customers according to their traffic
• buying/leasing a range of phone numbers to the government or bigger carriers
• setting up connections (over internet or private circuits) to other upstream/partner carriers

This is not an exhaustive list unfortunately :)

From my point of view, as a VoIP provider, we usually only use IP address auth between our SBCs and other providers. Could be over the internet or L3VPN/MPLS. In this case, we protect inbound traffic with ACLs to only allow these authorized IP addresses to reach the SBCs.

And as for customers, we provide SIP credentials and SIP proxy + registrar. The goal is for them to be autonomous and register the SIP trunk from anywhere they’d like. This way, we avoid the tickets asking us to change our side of the config because they changed their IP address for example.

I don’t see any pitfalls for either of these methods, for me the use-case is different. And thus each have pros & cons.