So with Apple's sales soaring because of the iPhone 4S, iOS 5.0, iCloud and one of its most popular Siri Voice Recognition technology is being ported to the iPhone 4
Hacker Troughton-Smith (@stroughtonsmith) an iPhone developer/hacker is working along side 9to5Mac (exclusive video on website) on this port
right now they have it running on the iphone 4 it recognizes your voice and dictation on keyboard
the only issue that they are running into is connecting the internet and Apple's servers to recognize commands and to answer questions via network
another problem is that it is running sluggishly on the iPhone 4 which is because due to a special GPU that was built to run iPhone 4S's Springboard and Siri itself
with this conclusion the iPhone 4's A4 processor can handle Siri which like Apple has done before with iPhone 3G not allowing for wallpapers to be used
stay tuned to more information as the porting progress continues of Siri, maybe it will be ported next to iPad and iPod (A4 processor or higher doubt the 3GS can handle this) on iOS 5.0
source: 9to5Mac