We already know that Siri does most of its processing server-side, and that Apple's claims of hardware as a limiting factor are tenuous at best. But new research from French developer Applidium reveals that Apple is truly full of it.
They've managed to completely reveal the entire process used for communications between the iPhone 4S and Apple's servers. In doing so, they discovered that the only thing keeping Siri from running on Android (or just about anything with a microphone and an internet connection) was a single line of code. Furthermore, they suggest that it's entirely possible to create a third-party Siri client that could fool Apple's servers into thinking they were talking with a normal iPhone 4S. Unfortunately, it's that single line of code that could severely hobble any attempt to capitalize on this discovery.
As it turns out, that code is unique to each individual iPhone 4S and as of now, there's no way to replicate it. So in order to get a third party-client working, you would either have to sacrifice a large number of iPhones, or risk easy detection by the Apple Gestapo. Basically, the only thing standing between you and a Siri-equipped refrigerator is a string of random characters.