Although not fully functional and quite difficult to use for ordinary iDevice's owners, Spire , tweak the assistant Siri brings the old Apple devices can be installed without any problem from Cydia, but comes with a small drawback namely the lack submenu "Siri" in the Settings application.
Well, if you installed your iDevice your spirit and the "Siri" in the Settings application is missing here is what to do for it to appear.
1. Open Cydia and add source smolk.myrepospace.com;
2. Once successfully added, look for "Syria for iOS 5.0.1" and install it;
3. At this point, if you access the Settings> General, you will see the "Siri" present among others.