Based on the success of IBM Watson and the amazing advances in tackling numerous hard tasks using deep learning in the past 3 years, I think a large high-tech company like Google or Amazon will create a useful conversational bot in no more than 10 years. (I've worked on the fringes of AI for 25 years and have followed the tech for even longer. These are exciting times.)
Initially, your very own AI companion ("Her"?) won't be capable of deeper philosophical conversation or insightful interpretation of novels or the human condition. But it will be able to write / speak in full paragraphs on topics like the best choice among 5 possible routes between point A and B, or summarizing the plot of a book or the gist of a news story, or why one product is better than another (e.g. based on assessing hundreds of Amazon reviews). And yes, it will be able to understand full spoken sentences from you, and generate both queries and answers.
I'm convinced such a bot will be useful enough that most of us will want one. Of course you won't need to buy a special piece of hardware, like the Amazon Echo. It'll be available via software on your smartphone, though the computing is likely to reside on the cloud (since that's where the data is).
Frankly, I think this is where the next innovations in smartphones will arise -- verbal interfaces that do a better job hearing and speaking and disambiguating using context about you and the kinds of questions you are likely to ask.