MuscleNerd, a member of the iPhone Dev-Team has indicated that a port of Siri from the iPhone 4S to other devices will likely require piracy.
Anyone hoping for a “port” of Siri from iPhone4S: pending a very low-level A5 exploit, it likely can’t be done without piracy 😦
(only way to extract Siri files from iPhone4S filesystem without pirating is to have the main FS keys, requiring low-level exploit)
Siri is an iPhone 4S only feature lets you use your voice to send messages, schedule meetings, place phone calls, and more. You can learn more about it here or see it in action here.