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by lxgr 1455 days ago
SMS gateways know the destination provider too, and I believe this is how blocking VoIP numbers is implemented in practice.
1 comments

Before I retired (2019), I was getting emails from our telecom providers that Canadian regulators were mandating that they not share porting information with customers (us), although it was generally available before, and was still available in other countries of interest (mostly US), for a fee.