When iPhone 4S was announced earlier this month, one of the mightiest features was definitely Apple's new voice control software: Siri. Siri understands normal speech, so you can send text messages and set alarms and so on by speaking to your phone. While Siri is purely software, Apple has limited it to iPhone 4S. Other supported devices can upgrade to iOS 5, but Siri will not be included. However, it has been widely expected that Siri will soon be hacked to run on unsupported devices - and that day has now come. 

Developers Steve Troughton-Smith (@stroughtonsmith) and @chpwn have managed to get Siri to run on iPhone 4 and fourth generation iPod Touch (uses the same A4 chip as iPhone 4, but has only 256MB of RAM). Even without the dual core A5 chip, Siri appears to run smoothly. Troughton-Smith said that Siri runs as fast on iPhone 4 as it does on iPhone 4S. The iPod Touch has some problems due to the inferior microphone (iPod Touch wasn't designed for calling like iPhone), requiring you to talk very loudly but the actual Siri software runs flawlessly. Below is a video of Siri running on the iPod Touch.

Owners of iPhone 4 and iPod Touch 4G shouldn't get too excited though, as Troughton-Smith says a public release should not be expected anytime soon. There may also be legal issues of distributing Apple's code, making a public release impossible. 

Source: MacRumors