Stroughtonsmith and chpwn have successfully ported Siri to the iPhone 4 and iPod Touch 4G. Earlier this month, Smith managed to get the Siri UI working on an iPhone 4, but now the hack is fully functional and able to communicate with Apple’s servers. A public release of the port is not on the calendar just yet, but it will eventually be possible to install Siri as a tweak through Cydia—but, due to the methods used to fool Apple’s servers, the legality of running Siri on non-4S hardware is still in the grey area.
Also, if you run across any tutorials on installing Siri, note that they are incomplete.
stroughtonsmith: I’d recommend you stay away from any instructions teaching you how to ‘install’ Siri; they missed a ton of steps and completely break the UI …not to mention, it doesn’t work in the slightest. It’s a fake port based on early temp work I did