That was a burner phone number and they're illegal in my country now.

I travel quite a bit and in most countries I'm required to show my passport to get a sim card. However, in several countries I've bought at least 4 or 5 sim cards by now (non tourist sims I mean) so there doesn't seem to be a limit on how many numbers you can have, they just want each number to be linked to a real person.

Of course it may be different in some countries, but it's worth checking to be sure.

No they're not.

Like, sure, you might need to register your name on it, but that doesn't influence the outcome of signing up for Amazon with it.