I just read this so I have not loaded it nor tested it. I’ll take a closer look later tonight.
http://blog.chpwn.com/post/14689740472
Remember it’s not a install and forget jailbreak app. You still need to set up a proxy so if you cannot do this yourself, hopefully you have some friends who do.

Update. I did some reading on how to get the proxy to work, and although its a nice solution, its not a full solution.  As such, I have to re title my post saying Siri for jailbroken phones is still not there.

Introducing Spire
Spire is my (along with Ryan Petrich) new tool for installing Siri on previously unsupported, but jailbroken, devices. Spire is a small download, but while installing it will download Siri itself (directly from Apple). Spire is available in Cydia right now — go get it! This will use about 100 MB of data, so please connect to Wi-Fi before installing.

However, Spire is not a complete solution. Apple still requires authorization to use Siri, so information from an iPhone 4S is still required. To insert this information, Spire allows you to enter your own proxy server address. I’ve put up a list of my ideas on how you might get access to a proxy; hopefully you can figure something out.