Google Instant is being rolled out to Android and iPhone users, in beta form. Earlier, Google had enabled the new "streaming search" functionality on a few selected Android devices (Droid X, Droid Incredible, Droid) earlier. Now Google has apparently approved it Android and iOS-wide.
Google's Instant search changes search results as you type. It's been available on the desktop for some time, but only now is coming to mobile devices.
For now, you need either Android 2.2 (Froyo) or and iPhones and iPod touch running iOS 4.x. Also, it's only available in the U.S. and English. More devices will be supported in the future, according to Google.
Meanwhile, we noted earlier when it was pushing out to a few selected devices that it didn't appear to work in anything but the native Android browser, not, for example, Dolphin. That seems rectified now.