iPhone experts Steven Troughton Smith and chpwn seem to have just gotten the iPhone 4S-only Siri working on jailbroken iPhone 4 and current-gen iPod touch units this evening. This bypasses earlier authentication issues. Theytweeted their success and posted a screen shot showing Siri working via Wi-Fi (the Airplane Mode icon just means that 3G is turned off, but it is possible to turn Wi-Fi back on even in AM; that’s what they did.)
Their success comes just weeks after the iPhone 4S debuted. Since Apple’s back-end systems are checking for iPhone 4S devices before processing Siri queries, they managed to work around this limitation. The hack is based on moving compiled code components from a 4S to the older units.