The hack requires a jailbroken device. By copying the app onto the device, the iPhone 4 can call up Siri and, more important, connect to the Siri servers. You can follow these instructions to install the app yourself and it seems to currently also work with the iPod Touch 4G although those instructions are forthcoming.
Mark: Do you ever see Siri showing up in Cydia (or another jailbreak store) for non natively supported devices?
Steven: No, I could not be a part of that. I have no doubts that others will package this up and distribute it quasi-illegally, or try and sell it to people. I am only interested in the technology and making it work; proving that it works and works well on the iPhone 4 and other devices
Mark: So, you also got Siri working on the fourth-generation iPod touch, how is that working out?
Steven: We got chpwn’s iPod touch up and running with Siri after proving it works on my iPhone 4. Unfortunately the microphone on the iPod is nowhere near as good as the iPhone – you will notice that the Siri level meter hardly moves when you talk to it. While it does work, you have to speak loudly and clearly to the iPod
We’ll give it a try this weekend and report back.