Even if we don`t have an official iOS 6 jailbreak, they updated SiriPort to support iOS 6. This means that you can currently install Siri on unsupported devices such as iPhone 4 running iOS 6.
SiriPort became official on iOS 5.1.1 and allowed people to get Siri working without the need of a proxy server.
All the queries are being ran through privately owned servers (in case you care about your privacy).
Note: You must backup your iPhone or iPod touch before starting.
Step 1: Jailbreak your device
Step 2: Add the official SiriPort repo in Cydia. To do this, launch Cydia, go to Manage – Edit – Add and type: http://repo.siriport.ru
Step 3: Go into SiriPort repo tab and find SiriPort (original) iOS 6
Step 4: Install SiriPort (original) iOS 6
Step 5: After you installed SiriPort, launch the Settings app and find the SiriPort (Original) section and you should see a button that says Install Certificate
Step 6: Reboot your device once your certificate it`s installed
Step 7: Invoke Siri and say “Hi”. Siri might answer after a few tries, but if “she” doesn`t, reboot your device and repeat this step.
If you followed all the steps, you have just gotten Siri working on your iPhone 4/3GS or your iPod Touch 4G/3G.