It's definitely a much worse experience for the recipient, I think new social norms of asking first are probably the best solution. I wouldn't ring someone who wasn't expecting a call without asking them if they were free to call first for example, and I think the same should apply to voice messages.

True, the latter is definitely a good change. I noticed it in work too, people don't call without asking first. It's really a great norm because you can say "just give me 5 minutes to complete this" when you're concentrating.

Of course it was never a norm before because text messaging didn't exist but it makes sense.

It would be great if people started doing that too for voice messages.