updated 01:40 pm EST, Tue February 14, 2012
Problems so far inconsistent
Apple may be trying to intentionally sabotage hacked versions of Siri, accounts received by iDownloadBlog suggest. The company has reportedly introduced a "SetActivationToken" into the system, creating problems for Siri hacks dependent on third-party servers, such as Spire. Difficulties have been inconsistent though, such that some users of the hacks have been completely unaffected.
A potential solution involves deleting the com.apple.assistant.plist file under the var/mobile/Library/Preferences/ directory. If Apple is trying to disable Siri hacks, it may be concerned about the amount of server traffic the users generate, and/or people complaining about Siri on unsupported devices. The only officially supported Siri platform is the iPhone 4S.