They should all be running filtering, although not all filtering is as effective as each other.

As you say, this is the legacy system, but it's still a huge problem for them!

My colleagues who do intrusion testing (for operators e.g.) tell me: We have not seen SS7 attacks in Europe for long time. The remaining attack surfaces are in the middle-east and north america.

That's promising! It's now 5 years ago, but Telenor had a fairly big outage caused by malformed SS7 inbound signalling. Not sure if there's been anything since, but it certainly was an issue relatively recently.

Hopefully with the (slow) move to 4G and IMS calling, we can turn the page on SS7 attacks soon.