With the October release of the iPhone 4S, Apple released a device that, despite having Siri, a significantly faster processor and more advanced cameras, earned some criticism for being overly similar to the iPhone 4. However, according to the Washington Post, the source files that form the basis of Siri are now available to be "jailbroken," or unofficially installed, onto the 4 without breaking copyright law.
The news source reports that tech aficionados had previously been able to add Siri's voice-recognition assistant capabilities to an iPhone 4, but the methods for doing so were illegal and difficult to execute. Due to the files released as part of Apple's latest firmware update to the iOS 5.0.1 operating system, Siri's files are exposed.
It is possible that this is an error on Apple's part, likely to be corrected in the near future. No reasons for Apple to deliberately permit open access to Siri have surfaced, and the company has not commented on the matter.
According to Cult of Mac, anyone wishing to add Siri to an iPhone 4 would require the skills necessary to extract the program's files from the decrypted ramdisks included in the iOS 5.0.1 update that power the iPhone's software-based smartphone accessories.