Developer Steven Troughton-Smith has made some progress on porting Siri voice assistant to the iPhone 4, reports 9to5Mac.

“Siri on the iPhone 4 can recognize spoken commands in both the standard Siri view and the keyboard Dictation view. The only issue at this point is that Apple is not authenticating (obviously) commands to its servers from iPhone 4 hardware. The Siri port to the iPhone 4, at this point, also has the ability to speak back to the user. You may notice Siri and the iPhone 4 acting very sluggish in the above video. The issue here is not Siri, but is that a special GPU driver for iPhone 4 is needed; and it is obviously not included in the iPhone 4S binary cache – where the Siri files are located.” We’ll keep you up to date on the progress of this port…

Here is a video showing this feat. It is “apparently” the iPhone 4, since you can notice the lag. However this is not confirmed yet.