Chpwn explains on his blog why you can not post Siri previous devices

We have several days mulling over the issue, why can not we use Siri on an iPhone 4 or 3G?

We have seen that the reason is not lack of power, Siri works exactly like an iPhone 4 in 4S, the reason is very simple, Apple wants to give exclusivity to your new phone. Some think that Siri will the iPhone 4 in an upgrade of IOS, but I disagree, I hope to be wrong, but Apple has left out features on other devices (wifi tethering, voice control, reminders geolocated ...) and has never introduced later.

Amid the confusion Chpwn, the first person to carry a fully functional Siri iPhone 4 explained why no one else has achieved and why can not publish it.

No one else has succeeded because this requires either the keys to decrypt the firmware or jailbreak an iPhone 4S, and he is the only one with a 4S jailbreak.

And you can not publish the copyright of Apple, if Syria was in the firmware of the iPhone 4 would only have to activate it, but it is not, is only in the 4S, so the only way to get it is to have an iPhone 4S hand or jailbreak iPhone firmware access 4S is public domain so we could all get it, but like I said, we still do not have the keys to decrypt it.

So the only way of not committing a crime is to have a 4S (your property) to jailbreak, but if you do not need the iPhone Siri 4, or decrypt the firmware at your own risk and install Siri, but right now that is impossible.

We can only wait.

(Read the full article here)