If your website is down, your mail relay may be down, making e-mail unavailable. The phone is also a much better way to contact someone immediately, which you might want when your website is down.

If you rely on your visitors to phone you when your website is down you are doing something very wrong.

Once I worked for a company where part of the website had been compromised by an attacker, and was being used to host some malware. We only found out when a random visitor found it, then looked through the site and found a random support address (which was supposed to be internal-only), and sent us an e-mail to tell us about it, which luckily generated a ticket which we eventually reviewed.

We would have preferred someone called us immediately, in case we didn't see the ticket immediately. But we didn't have a security hotline publicly listed.

Putting a phone number in a big public directory of phone numbers for when e-mail doesn't work isn't a bad idea, regardless of what anyone (including the EU) says. We've had phone books forever. This is just a phone book for domains.

Well, that's a case for how it should be opt-in, though.

Agreed.

"My website is so critical that I want random people to be able to call me about it" is an oxymoron I don't think anybody has ever said.