We never reported people who have ported Siri to the iPhone 4, iPod touch 4 and iPad, but in fact the only thing they’ve ported or install is Siri’s GUI. Follow this tutorial, You’re going to have the same siri with iPhone 4S on your iOS device… 

Note: that this is only the GUI ( graphical interface ) of Siri, and there’s no actual functionality added to the device. Also please note that there’s a possibility that your device will end up in a respiring loop. So do this at your own risk…

All the things You need:

*iPhone 4/3GS or iPod Touch 3G/4 running iOS 5 jailbroken ( tethered )

*OpenSSH

*MobileTerminal

*Link Identity Editor ( Cydia )

*SFTP client ( like Cyberduck for Mac or iFunBox for Windows )

*iFile ( Cydia )

NOTE: You'd better back up your files via iTunes before doing this:

Step by Step Guide:

1. Download and extract this file to your desktop

2. Via SSH browse to /System/Library/PrivateFrameworks/ and copy the AssistantServices.framework folder

3. Load MobileTerminal, and type the following commands

chown -R root:wheel /System/Library/PrivateFrameworks/AssistantServices.framework
chmod -R 755 /System/Library/PrivateFrameworks/AssistantServices.framework
ldid -S /System/Library/PrivateFrameworks/AssistantServices.framework/AssistantServiceses

4. Via iFile go to  SpringBoard.app and find N90AP.plist ( iPhone ) or N81AP.plist ( iPod Touch ) and open them as text and add

720p

1080p

assistant

5. Respring your device

Video Guide: