Apple's not going to happy about this one. It's been confirmed that a bunch of Chinese hackers have successfully ported Siri to jailbroken iPhone 4 devices — full voice-activated personal assistant powers in tow — pinging Apple's servers with illegal binaries.
For some reason (most speculate it's a CPU and battery-related one) Apple's keeping Siri's personal assistant powers locked to the iPhone 4S.
We won't get into the details on installing the hacked Siri onto your iPhone 4 (we haven't tried it ourselves), but the full-Siri experience is called H1Siri and is available after you add a custom resource repo to Cydia.
Unlike Steve Troughton's Siri port to iPhone 4, H1Siri can actually ping Apple's servers and pull data from it. H1Siri is said to work on all models of iPhone 4 (CDMA and GSM) running iOS 5.
If you're not afraid to take a walk on the dark side, then know that this hack has been confirmed to be using copyrighted binaries and that you are transmitting personal data to Apple, with the possibility that your data is also beingrecorded through unknown Chinese servers.
We highly advise not going the illegal route to get Siri on your iPhone 4. We view H1Siri as merely a proof-of-concept that Siri can run on non-iPhone 4S hardware.