In Short: Google will now record select calls initiated via call-only ads or affiliated call extensions, in the United States only, in order to ensure that the ads behind those calls are not spam or fraudulent, and to help improve the user experience. When you get into a call from an ad link or any other call that's otherwise initiated via tools in Google's advertising platform, you will hear a notification that the call is being recorded by Google, giving you the opportunity to hang up if you're not comfortable with that. To be clear, not only will you be notified, but only a small percentage of qualifying calls will actually be recorded, and only calls initiated via Google's ad platform will qualify.
Background: Google has allowed advertisers to use ads that will initiate a phone call when interacted with for some time now. While Google's service can vet the ads that initiate those calls for quality and to prevent fraud, malware and other bad faith acts, the same could not be said of the resulting phone calls until now. Otherwise innocent-looking ads could lead to a call where a sales agent makes false promises and goads users into ponying up, for example. This initiative is there to help put a stop to all of that, as well as to help advertisers screen what kinds of customers may be interested or move further along in the process, and how to tweak their ads and the calls those ads start up going forward.