Spire is now available in Cydia, you can get this tweak for free. But one thing to note before proceeding, it still requires the needed files from Apple servers, this is the problem, which means you need Siri proxy setup and then iPhone 4s. Well, why we still need Spire if we own iPhone 4s, fyi I don't have that A5 device! If you don't you can borrow it from your friends who own it, right? Anyway you can get Spire Siri proxy server for free.
Because it's requirement you can avoid -- the process will require you are going to need to enter your own proxy server address via iPhone 4s.
How to install Spire from Cydia
To install Spire package, launch Cydia and then search for Spire, of course install it. No need any repository because the tweak is listed under BigBoss repository by default.