[axelthegerman]

Some folks build (or use) telecommunication systems that work for (cell) phones. Believe it or not but for receiving a notification via text message you nobody needs to install any apps or even require a smartphone and/or internet access :)

[alwayslikethis]

It's still mostly used for malicious tracking. In many countries you have to use your identity to get a phone number, and SMS verification exploits this to track users.

[flangola7]

Never heard of getting a convenience store burner phone for cash?

[miskin]

This is not possible in most of EU markets, KYC is mandatory and even prepaid SIM cards must be registered and verified with ID before SIM is used for data or calls. Old SIMs without registration were blocked until they would be registered. Some exceptions may exist, but this will be harder and harder in future.