This tutorial will give you instructions for how to port Siri onto your iPhone 4 or iPod touch 4G without a proxy. Again, you'll need to have your iPhone or iPod jailbroken.
Open up Cydia, go to the Manage tab, click Edit and add the repo source http://repo.siriport.ru
You'll now see the new source in your list. Browse the new repo source and install the Siriport app. It may take a few minutes. Be patient. Once the installation finishes, you will be told to reboot your iPhone/iPod.
Once you have repooted your device, you'll need to install an iPhone 4S certificate. Open this link in Safari http://siriport.ru/1.crt
If that link is no longer available, here is a rapidshare link for it. Save it and e-mail it to your iPhone or iPod.
This will bring up a certificate installation window. Tap on the install button. Siri is now ready to be turned on.
Go to Settings and then General. You should now see the Siri option. Open up the Siri menu. Turn Siri to On.
You should now have a working Siri port on your iPhone 4 or iPod Touch 4G. This may work on the iPhone 3GS as well but I do not have a phone to test it on. If you have successfully been able to port this on an iPhone 3GS, please let me know. Thanks!
Disclaimer: I have tried this on my own iPhone 4 and it works. However, I will not be held responsible if something goes wrong. Please proceed at your own risk.