New legisation is being enacted around this on an ongoing basise: e.g H.R. 4998 was introduced about two weeks ago

All the major carriers are implementing a STIR/SHAKEN strategy that should be in effect by next year. But it is complicated to do and there may still be problems when they do - as others have explained here it's not as simple as it first appears.

I don't have any sympathy for the operators in this. They've profited from this for long enough and ignored the problem. There's a lot of pressure on them to solve it and the impression I have is that there's no appetite for "the dog ate my homework" excuses from regulators so let's see.