Spire was an innovative and useful tweak to use if you would like Siri on iPhone 4, 3GS, and other iOS 5 Devices. Apple took some measures against it. Now?
The answer is AssistantConnect4S and AssistantConnect.
AssistantConnect4S sends your certificates to other non-iPhone 4S users via E-Mail. The receiver can use those with the AssistantConnect to use Siri with Spire installed.
If you know somebody with jailbroken iPhone 4S (and you have iPhone 4 or 3GS) ask him to send you the certificates at your e-mail and use AssistantConnect to enable Siri.
(The iPhone 4S user is recommended to send only to 5 other users his certificates so as not to be blacklisted)