Not allowed. The same government rules that stop Google from refusing calls from Apple devices also stop them from refusing calls from whoever is doing this. The government would have to update the rules. They could mandate number verification for all calls, even those passing over TDM trunks, and make it the network's problem to figure out how to do that. The rules currently say that all calls which don't pass through legacy equipment must have verified numbers, so there's a market for making calls take stupid legacy routes on purpose.