Siri is no longer the monopoly of iPhone 4S. Now you can use Siri on all iOS Devices and with a new app called Spire.
A trio of iOS developers: Grant Paul (Chpwn), Ryan Petrich, and Steven Troughton-Smith have recently released a new Siri port called Spire. This port can mirror all the iPhone 4S Siri functionality. Spire can make Siri work on iPhone 4, iPhone 3GS, iPod Touch 3G, iPod Touch 4G and iPad (first generation).