Siri, the killer app for Apple’s latest iPhone, has finally come to older iOS devices. Thanks to Grant Paul (aka chpwn), a developer in the iOS jailbreak community, a free (and legal!) port of Siri called Spire was released late last night to the Cydia store (the App Store for jailbroken phones). The port is not quite perfect, as Siri’s servers require identifying information from an iPhone 4S. So people who want to install Spire will have to obtain identifiers from a 4S before they can get it set up on their phones. Paul has several suggestions on how to do that on his blog, where he announced the release.

This new app capitalizes on what appears to be a pretty significant mistake by Apple. Two weeks ago we ran a story on a mysterious update to the iPhone’s operating system. Though it was eventually found to be a fix for a SIM card problem, no one was quite sure what this update – a newer build of the current iOS 5.0.1 software – was supposed to do. One thing was clear however: Apple had left the iPhone’s file system unencrypted. That meant that the jailbreak community could get to iOS’s basic files without breaking Apple’s encryption, and therefore without breaking copyright law. In effect, Apple had gift-wrapped Siri, which has been giving jailbreak developers fits since the iPhone 4S released earlier this year. The unfettered access to the file system allowed direct access to the files underlying Siri, clearing the way for the software to be ported to older iOS devices. Spire reportedly runs on a range of devices, including the iPhone 4 and the first-generation iPad.

Here is Paul’s announcement on Twitter:

Older iOS device users, would you jailbreak your phone to get Siri? Let us know in the comments.