Singapore does this. Any message that comes from an unregistered sender show up on the phone with “Likely Scam” as the sender name.

The Australian one will label them as Unverified.

Personally, I'd prefer them to be blocked. If it's important and legitimate, they'll register.

	▲	wizzwizz4 3 hours ago \| parent [-]
		There are good reasons to allow unregistered telecommunications. If you don't like it, you can always block it your end; given that we can all expect many other people to do the same (and it'll likely be a feature built into many phone operating systems), the social pressure you're after still exists.