There have been many reports and even a confirmation from @chpwn that Spire would no longer work on iOS 5.1.1 (jailbroken) for iPhones and iPads. That doesn’t however mean that Siri won’t be available on the iPhone 4/3GS devices running iOS 5.1.1.
Here’s how to install Siri on iPhone 4/3GS or iPad, iPod touch 4G without proxy. You don’t need to buy Siri proxies here (as in Spire). All that you would be doing is adding a repo, getting a certificate and that should do it. Folow the steps to Install Siri on iPhone 4/3GS Running iOS 5.1.1