Too bad they (and other phone manufacturers) don't protect phone calls with some kind of end-to-end encryption.
Apple asserts that Facetime and Facetime Audio are end-to-end encrypted. And Google claims Hangouts are encrypted as well.
I don't know whether there are caveats (or how many) to either of those claims. But that's about as much as one could hope for in the current climate. [2]
[1] Particularly upstart computer companies dealing with the telecom oligopoly. Long cozy with governments and law-enforcement, if not an explicit part of government.
[2] It's a serious bummer that FaceTime never developed into the open standard they claimed at introduction. I've been curious about where that fell apart. (Competitor disinterest, patent liability, carrier terms, etc)
All of this is a damn shame because in my experience the competing standards don't have the usability and quality that FaceTime provides.