Spire is my (along with Ryan Petrich) new tool for installing Siri on previously unsupported, but jailbroken, devices. Spire is a small download, but while installing it will download Siri itself (directly from Apple). Spire is available in Cydia right now — go get it! This will use about 100 MB of data, so please connect to Wi-Fi before installing.
However, Spire is not a complete solution. Apple still requires authorization to use Siri, so information from an iPhone 4S is still required. To insert this information, Spire allows you to enter your own proxy server address. I’ve put up a list of my ideas on how you might get access to a proxy; hopefully you can figure something out.
Spire uses a new method to obtain the files necessary for Siri, so it doesn’t have the copyright issues encountered by previous attempts. Similarly, rather than directing all traffic through a specific proxy server (and the associated privacy issues), Spire allows you to specify your own proxy server.
Thanks to planetbeing for PartialZip and Ryan Petrich for his fixes and improvements.