Developer Steven Troughton-Smith seems to have made a bit of a breakthrough in porting the Siri voice-recognition system onto the iPhone 4 - showing that there's no good reason why Siri couldn't run on the iPhone 4S predecessor.
The developer has been working with 9to5Mac in order to make the Siri switch, and it is an impressive bit of work.
The iPhone 4 version of Siri can apparently carry out commands, both when vocalised and when typed, and the Apple voice-recognition system can also talk back to users.
From the video it may seem a little slow, however the issue is apparently nothing to do with Siri itself, as 9to5Mac explains: "The issue here is not Siri, but is that a special GPU driver for iPhone 4 is needed; and it is obviously not included in the iPhone 4S binary cache - where the Siri files are located."
In terms of suppport, the iPhone 4 seems to be doing a fine job, with the original A4 processor said to be powerful enough to carry out the task in hand. However, it's not really a surprise that Apple is holding out on iPhone 4 owners as a native - and faultless - experience is usually top of its agenda.