Android/iOS: Every major operating system these days comes with its own personal voice assistant, but most of them are stuck on a single platform. Hound, the assistant from SoundHound, is available in beta for Android and coming to iOS — but Aussies will have to wait a while to enjoy it.
The service promises many of the same types of searches that you'd perform woith something like Google Now or Siri. However, SoundHound says it can handle much more complex commands like "show me four or five star hotels in Seattle for three nights starting on Friday between a hundred and fifty dollars and two hundred and fifty dollars a night." If it works that well for all the many, generalised commands users can throw at it, the app is a lot more flexible than some current voice assistants are. That said, it will clearly take some time to develop.
The Android version is in an invite-only beta right now and is restricted to US users, so if you're keen to try it you'll need to do some serious hacking on your Google ID. The iOS version is currently in development and you can also sign up to be notified at the same link.