But if none of method works for you, perhaps you can try what GreenRiver SiriServer. It is another free Proxy Server to install Siri on older device.
And the great thing about GreenRiver SiriServer is doesn't take any iPhone 4s authentication tokens. GreenRiver uses GoogleSpeechAPI that takes speech packets and then convert them into speex codec to be sent to Google for processing purpose. After Google finished the process, it will then send what you spoke in plain text, and of course to use this service your iOs device must already be jailbroken first.
Now let's get into the steps to install Siri On iPhone 4, 3GS, iPod touch 4G with Google Speech API using GreenRiver SiriServer.
Step 1: Firstly jailbreak your iOS 5 device first if you have not, you can user Redsn0w to jailbreak iOS 5 device of yours.
Step 2: Open Cydia, and search for Spire via BigBoss repository. Once you found the tweak, then install it. The file size is 100MB, so be patient while waiting for the installation process.
Step 3: Once the installation is complete, then reboot your iPhone.
Step 4: After Spire is installed, now get the new certificate (remove the old one if exist). To do so use your iPhone Safari browser and then open this url: http://siri.grwh.net/newca.pem in order to install the ceritificate.
Step 5: After you have managed to installed the certificate, then go to Settings > General > Siri and enable Siri to On (to enable Siri on your device).
Step 6: Now go to Settings> Spire and then add this Server Address there:
https://siri.grwh.net:1221 or https://siri.grwh.net:1222
Step 7: Now say “Hello Siri" while holding the Home button, if the voice assistant app responds your back saying Hello, that means you are connected. However a user say he waited until until 24 hours before the Siri finally work.
Anyway you can the list of Siri available commands from this link.