As we wrote in an earlier this week, @Jackoplane successfully ported Siri to the iPhone 4. He is now working together with @joshmtucker, a member of ModMyi, and @iH8sn0w on their port.
They just released a video showing an iPhone 4 running Siri:
Disappointingly, it doesn’t show any functionality of Siri other than showing up if you hold down the Home Button. There is currently no sound (not enabled in this particular build), and we didn’t see Siri connecting to Apple’s servers. Hopefully they will release another video showing a fully functional port of Siri on an iPhone 4 soon.
There is still no ETA, but @joshmtucker wrote in his FAQ that it should be within the next weeks.