theoretically the phone could still record all audio and then sync with the cloud when back online, but I'm grasping at straws here.
Regulations are great, but I prefer to have both kinds of defense.
I agree that hardware switches are ideal, but I don't see them being common since most of the folks pushing out phones want to use those devices to collect data on the people who buy them.
If your threat model is governmental, then that's a whole different thing entirely. You'll have to go to true extremes to even have a chance at defending against that. For instance, you shouldn't have a cell phone at all.