Siri has been ported over the iPhone 4...kind of. 9to5Mac report that a developer they have been closely working with has ported Siri over to the iPhone 4.
However, as always, there are some issues. Siri is able to understand the commands which a person gives it however the Apple servers do not allow the iPhone 4 hardware to access the data needed for carrying out commands. The port has made the iPhone 4 act very slow and lag in many ugly ways. This is because of a special type of GPU driver needed which is only available in the iPhone 4S.
Apple have pulled a sly one over here. It can work on other "iDevices" but the company have obviously made it exclusive on the iPhone 4S to make it one of its unique selling points. Boosting sales and upgrades = more cash.
Within hours after posting this article, the developer behind the port has drastically improved the performance of the original iPhone.
The video above shows how laggy it really was.