Steven Troughton-Smith actually announced yesterday on Twitter that he had managed to pass the authentication from an iPhone 4.
It is this developer who announced two weeks ago that he had ported the Siri executable to iPhone 4. But Apple's servers then refused to process requests that did not come from an iPhone 4S.
But he finally figured out how to get around this purely arbitrary limitation from Apple, in "one line of code (plus a ton of file system modifications)". All the more arbitrary as "Siri is literally as fast on the iPhone 4 as on the 4S", according to him. chpwn, designer of Cydia who contributed to the port of Siri, indicates that it is "slightly slower on the fourth generation iPod Touch, but that only the interface is concerned".
Remember that the user's voice command is transmitted live (streaming) to Apple's servers for processing. The superior performance of the iPhone 4S therefore has only a moderate impact on Siri, when it responds by text-to-speech.
The hack will only be made public once it has been confirmed that it works fully, does not break anything else, and is safe. Steven Troughton-Smith will not distribute the files he edited, which is illegal, but will instruct how to replicate his approach from the iPhone 4S firmware IPSW file, or directly from an iPhone 4S, when it will be unbridled (jailbroken). No date is naturally advanced.
The main differentiating point of the iPhone 4S will soon no longer be one. Siri is indeed perfectly functional on iPhone 4 and even on the fourth generation iPod Touch, after applying a hack that has not yet been made public.