Midler v Ford: https://law.justia.com/cases/federal/appellate-courts/F2/849...
Waits v Frito-Lay: https://law.justia.com/cases/federal/appellate-courts/ca9/90...
One interesting thing is that these cases are really deep in common law. They are quite far removed from statues, and statues are cited in the opinion only to argue how they don't apply.
In these cases, the voice was "distinct", and they intentionally copied it. It's possible these don't apply to ScarJo, although the fact that they negotiated with her is a bad sign, since that was also a common fact in the prior cases.