In case you have mistakenly updated your iOS to iOS 5.1, Spire will stop to work as this Siri port is not updated by its developer, chpwn, to keep up with iOS 5.1. But fortunately there is a solution for the said problem. You can grab Spite, the Spire's alternative that can be used by iPhone running on iOS 5.1 firmware.
Spite is a Cydia tweak created and developed by TechNetec and it's still in beta stage, therefore don't expect too much. And to install it, a tethered jailbreak is required. Currently Spite is in version 2.2. The updated version of the software allows for an uninstall without restoring in iTunes.
How to install Spite on iPhone 4 iOS 5.1 / 5.0.1 / 5.0 (or on iPhone 3GS, iPod Touch 4G, iPad).
Step 1: Tethered jailbreak your iPhone, iPod, iPad first using Redsn0w, to verify the version of iOS your iPhone is running.
Step 2: Now add the Technetec's url repo --- Manage > Sources > Edit > Add:
Step 3: Afterward, now search the Spite 2.2 and then install the app. The total size of the Spite is 150Mb.
Step 4: Reboot your device.
Step 5: To make Spite works, you still need a Siri proxy, therefore find one on the internet or borrow from your friend that owns iPhone 4s.
Hope this post helps and see you again!