Thanks to chpwn and Steve Stroughton-Smith, Ryan Petrich has successfully shown off a proof-of-concept Siri port on iPhone 3GS. It doesn't work as well as the iPhone 4 port, mind you, but that's easily overshadowed by the sheer coolness factor.

No word on how or when, if ever, this will come to an iPhone 3GS near you. Whether due to beta-status, server load, Nuance licensing restrictions, or simple product differentiation, Apple has chosen to keep Siri exclusive to the iPhone 4S

Source: @ryanpetrich via @stroughtonsmith