This is going to be awesome/terrible for social engineering attacks. We'll be training millions of people to to trust phone calls from "Google". But are you talking to Google-calling-on-behalf-of-your-boss, or Google-calling-on-behalf-of-some-phisher? Or better yet, some custom system that pretends to be Google over the phone? Who knows!
Google Duplex can do the same thing - without even staffing a call center.