Warning: Not my own post
@MrAjsTech has posted a video showing off Siri on his iPhone 4 and iPod Touch 4G using a port he is developing. He is the lead developer of the i4Siri Project along with @leftyfl1p. The project i4siri is going to bring Siri to older devices. These devices include iPhone 4 and iPod Touch 4G. Potentially this port could be used on the iPhone 3GS but there are no confirmations. The overall goal is to be able to use Siri on these older devices without the regeneration of 4S auth keys.
They hope to be able to create a server that will allow users to connect when they have his cydia tweak installed. This tweak will enable a Siri GUI along with connecting the siri proxy server. Since this server is not apple’s there will be no blacklisting like h1siri.The iPhone 4 is 100% working. MrAjsTech also mentioned that he had issues with the root partition size on the 8GB iPod Touch 4G. It seemed that the native partition size that holds the iPhone OS was not big enough to hold the bigger cache file for the Siri port.
This port looks very promising. As for a release they are hoping to release the port first for people who have an iPhone 4S and then we will move on to getting the Siri Proxy server up and running. They plans are to work around the fact that the distribution of Siri files is illegal. Extracting the code from the 4S IPSW looks like the most promising solution.
If you want to more about this port check out the official i4Siri site.