In December, we reported that Siri could be used on any Apple device with the help of Spire. Spire would not let Siri remain exclusive to iPhone 4S.
Following the release of the iOS 5.0.1 untethered jailbreak, many rejoiced with the release of Spire, a simple Siri installer that was developed by iOS hackers Grant Paul and Ryan Petrich. In iOS 5.0.1, Apple made a mistake that allowed hackers to exploit a cache file for gaining access to the files necessary for making Spire a reality.
Although we have a tethered jailbreak for iOS 5.1 now for non-A5 devices, you will notice that the Spire cannot be installed on iOS 5.1 as Cydia will not allow you to do that. This is because iOS 5.1 does not support the iOS 5.0.1 version of the frameworks. Alternatively it supports only the iOS 5.1 version of the frameworks. The iOS 5.0.1 frameworks were easy to exploit as Apple handed the files to hackers on a silver platter, unencrypted, and made it very straightforward to create an automated downloader for them.
Citing Ryan Petrich, it is extremely likely that we will not see a Spire Siri installer for iOS 5.1, irrespective of the nature of jailbreak (tethered or untethered) because writing the installer would be less straightforward and much more difficult. If you are on iOS 5.0.1 and happy with your untethered jailbreak and Spire Siri functionality, you should not upgrade to iOS 5.1.
Those of you that do not use Spire regularly, probably would not have to worry about upgrading to iOS 5.1 or any newer firmware for that matter when a newer jailbreak for the corresponding firmware is released. Hackers are actively working on finding exploits for Apple’s newest firmware, iOS 5.1.