It would work until you need to route an international call.
And there's a lot of telemarketing and scams happening across country lines.
I mean, they should still do it. It's just the first problem they'd face.
That's fine. International calls pay a dollar a minute. If telemarketers had to pay that they'd be out of business.
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In Finland international inbound calls using Finnish caller ID are simply blocked (mandated by regulation since 2023).