Engadget caught wind of the fact that Apple has filed a patent for an "intelligent automated assistant," which sounds like the nice lady (or man) in your iPhone (or, as of iOS 6, iPad 3) called Siri. The application talks at length about a digital assistant controlled using speech (it's Siri), which takes a user's speech input (again, it's Siri) and then fulfills the speaker's request using digitized speech. In other words, a patent for Siri.
Unfortunately, because the patent is so general, there isn't a whole lot of nuts-and-bolts talk about how Siri actually works -- at least none that we didn't know already. But there is some reference to the term "anchor phrases," which are words and phrases that Siri looks for in your speech to actually figure out what you're saying. The patent also talks about providing alternate words to the user in case something can't be understood, and the use of databases (like, say, Wolfram Alpha) for figuring out which information is needed by the user.
Apple's all covered, then, should it ever face the question of Siri's origin in court. This patent, plus any others that it may have picked up when Siri was acquired, should be more than enough to defend its case.