What you are saying totally makes sense, but numbers are portable as mjevans pointed out and b-number analysis is a bit more primitive. This requires cooperati

What you are saying totally makes sense, but numbers are portable as mjevans pointed out and b-number analysis is a bit more primitive. This requires cooperation from all the telcos and would require business changes, process changes and code changes to systems so that you could approve-list what is a mobile network NPA/NSX and deny-list what is not. This just means spoofers would only be spoofing mobile numbers. Now you have a game of whack-a-mole. Some of these systems are so old that the people that wrote code for them are long gone. I am not saying that is universally true of course. Some switches had fairly modern hardware. But unlike the internet where everything peers with bgp and information / routing information is freely shared, there is a lot more manual work and manual changes and coordination required. Even if you could update all of them, now you have to maintain yet another real time deny-list and that does not really solve spoofing.