The cat and mouse game between Apple and the devs has moved up a notch. With Apple saying it would never support Siri on anything than a 4S, MuscleNerd (who any self respecting jail breaker would be aware of) has announced that it appears to be possible "legally" on the iPhone 4.
This is all down to Apple's iOS 5.0.1 update that is an official release pushed out by Cupertino but also has an acceptable encryption key for its main file system. That basically means you can browse its inner workings from a PC and therefore you can get open access to system files, previously encrypted, which allows a Siri port.
MuscleNerd's tweeted on the issue: “to clarify: wide open for inspection from a Mac/PC…not wide open security wise :) Can get Siri files and such without piracy”.
It negates the need for an iPhone 4S unique identifier with a key being rotated every 24 hours to keep it hidden. The problem was that if too many phones started calling Siri from a single 4S identifier, Apple could have identified it, killed the port, thank you and goodnight.
No doubt Apple will soon start changing things again. Until then, it's one up to the devs.