It depends on what you're going for. Relatability seems to have been a major goal of the people who designed the AIs in "Her"; telepathy not being a particularl

It depends on what you're going for. Relatability seems to have been a major goal of the people who designed the AIs in "Her"; telepathy not being a particularly notable human trait, I think it's reasonable to understand why they might choose a vocal instead of a neural interface. (Especially since the movie is intended to make a point about today, when there is no such thing as a neural interface, but people talk to Siri or Google Now all the time.)