"...there is a downside. Could you imagine artificial personas used in telephone scams or phishing situations? A help desk knowing some information and then asking for verification of other data?"
I've already received calls like this on my phone. The first time caught me by surprise, because initially the voice seemed to be interacting as if it were human. It was only when the voice response (AI?) system got a response from me that resulted in an odd statement from the "caller" that I figured out it was fake. So, for my money, the Google Call example is already going on for groups trying to make a fast buck on the unsuspecting.