SiriSn0w does the same thing as other custom firmware creators like Sn0wbreeze, but it installs Siri alongside Cydia. It also installs the new corona untether by pod2g. So you can turn on your device without a computer.
@ReagentX and @ChristopoulosZ just released a new Cydia repo with a package called SiriN1ght that lets you install the Siri UI on your iDevice, just like sirisn0w. It does currently NOT connect to Apple’s servers due to the missing authentication files. The difference to sirisn0w is that SiriN1ght contains the actual files copied off an iPhone 4S, whereas sirisn0w used some fake frameworks in order to work.
As soon as the authentication files are available (jailbreak for the iPhone 4S required), this package will most likely get updated and will hopefully finally bring Siri to our older iDevices.
I personally would not recommend to install this package as you only get the User Interface and the chances of breaking your iDevice are pretty high. There were a lot of people complaining about respring loops when sirisn0w was released, this could happen with SiriN1ght as well.
If you still want to install SiriN1ght, just add http://cydia.zchristopoulos.com/ in Cydia.
Warning: SiriN1ght is incompatible with Semi-Tether. So you should either not install SiriN1ght or first uninstall the Semi-Tether to avoid a respring loop. @ChristopoulosZ also tweeted that you cannot uninstall SiriN1ght, you have to restore your iPhone.
@StanTheRipper, the developer of Sirisn0w, recently tweeted that he organized some Siri files. Two hours later he tweeted that Siri almost works. Like you see in the picture on the left, Siri now tries to establish a connection to Apple’s Servers, but it doesn’t yet succeed. Siri now also talks to you.
StanTheRipper also tweeted that he can’t release the files due to copyright issues (Read chpwn‘s blog post for more details). This means that we may not see Sirisn0w being updated in the near future.
StanTheRipper uploaded a video showing the current state of his port on the iPhone 4:
@StanTheRipper released SiriSn0w, a package for Cydia that will install the Siri UI on your iPhone 4. I still would NOT recommend installing this package or any other Siri UI, as it doesn’t connect to Apple’s servers and therefore is useless.
WARNING: There are a lot of people who report that their phone is stuck while respringing. I would wait to install this package until all the bugs are cleared out.