The Siri-like update to Google's Search (https://itunes.apple.com/gb/app/id284815942?mt=8) app for iOS is now available for download at the iTunes store & iDevice. I have just tried it on my iPhone 4 and it's fantastic! As shown in the video above, it's really snappy with the search and voice recognition; even with the fourth generation iPhone (non-Siri iPhone). Now if you're located outside of the States or your default language is not set to English (U.S.) then the when you use the Voice Search, you won't get the answers spoken directly back to you.
To turn this on, first tap on the Settings icon located top right.
In the Setting page, tap on the Voice Search label.
In the Voice Search page, turn on Voice Search, select your language to English (U.S.), and then you'll see the option for Speak answers back is now available.
Turn it on, tap on the Done button and that's it. You now have Voice Search fully loaded.