The new app, called Spire, is available in the Cydia app store via the Big Boss repo and is compatible with the iPhone 4, iPhone 3Gs, iPod Touch 3rd and 4th gen, and 1st gen iPad. It's a good idea to install Spire while on WiFi, because part of the process is that Spire will download 100 MB of data, some of which comes straight from Apple's servers.
This isn't a complete solution as Siri does still require info from an iPhone 4S to work, but Spire gets around this by allowing users to add a simple proxy server. There are some proxy servers set up for use, or if you know an iPhone 4S user that won't mind you using their token, you can do that as well. Or, pretty soon it seems that Chpwn is planning to set up a dedicated proxy server, and charge for access.
source: Chpwn via Smash iPhone