I use my Android's voice control daily. It follows a different philosophical model (as the Google guy said, it's the Star Trek versus the Star Wars model, which is a comparison that is apt), however the result is a device that does the majority of what I want perfectly. I am never guessing at the limits of its lingo (all current natural language systems have limits, which is why they are so uncommon) because I know the specific commands that do the things I want.
The real competition to Siri is that people don't want to treat their phone as a human. That the slow imprecision of spoken language is only a worst-case substitute for alternative options.