It's not true, there is many physical SIM providers that provide APIs, so Agents would use it the same way. This repo still requires an external provider, so it wouldn't change anything.
When you go at that scale of providing phone numbers to agents giving or handing them physical SIMs out, it isn't the best possible way. The best possible way is making it very agent-centric. For physical SIMs, AT&T and Verizon are already there. but agents can't buy numbers from them hence something which is very agent-centric is needed. Even after you acquire a phone number from these providers, you need to SIP trunk those numbers then you hit the regulations of A 2P and 10 DLC for SMS. There are robotic calling regulations above that. There are plenty of regulations in there and your agents cannot deal with them. What AgentLine does is give the agents phone numbers using simple skill file. That's the main proposition. Yes definitely it will require an external provider because you cannot build a telecom infrastructure overnight.