A correction has been made to this story. See below for details.
As mentioned in an earlier post about the upcoming firmware update for T-Mobile's G1, the built-in Google search tool is getting voice-powered search. Like Google's rule-breaking, first-party iPhone search application, users can simply talk into the application to have their queries transcribed into text.
The big difference, however, is that users will need to begin a voice search by tapping the microphone icon instead of simply holding their phone up to their face.
Why is this you ask? The G1 is missing the oh-so-important proximity sensor, which on the iPhone tells the application you're holding it up to your face. Also, the app doesn't make use of the G1's accelerometer, which means it can't fake knowing you're lifting it from palm to head. In the iPhone iteration, the application uses both of these sensors in tandem to do its voice searching magic.
Correction: This blog initially misstated why the G1 app does not allow you to just hold the phone up to your face. The T-Mobile G1 does have an accelerometer, but the application does not make use of it.