Zuckerberg just posted this on Threads. Federation seems to be coming relatively soon.
Starting a test where posts from Threads accounts will be available on Mastodon and other services that use the ActivityPub protocol. Making Threads interoperable will give people more choice over how they interact and it will help content reach more people. I'm pretty optimistic about this.
It might not be very useful for spoofed calls, but I can see the use to block harassers. You block once, and they are block in the phone and messages app, and also are blocked on your other or next devices.
Also, I think the block list is not shared between users, only between your own apps and devices.
People mostly go where other people are.