Although the iPhone 4S might be dismissed as nothing but a spec bump phone, it does have one distinctive advantage over every other smartphone out there: Siri. Anyone who wants to compete with the iPhone 4S (and, presumably, the future iPad 3) will have to come up with their own answer to Siri, or be lost.

Well, what do you know. The hunt by Apple’s competition to find small voice recognition startups and absorb them has already begun with the revelation that Amazon has already picked up a company in the hopes of launching their own would-be Siri-like speech recognition service.

Using a shell company known as Dion Acquisitions Sub, Amazon has picked up a company called Yap according to newly revealed SEC filings.

Yap was a voicemail-to-text service that was focusing heavily on natural-language speech recognition with an emphasis on mobile technology… the perfect background to bring a Siri-like interface to future Kindles, including the Kindle Fire tablet line. In fact, you may already know Yap from their iOS app, which was removed from the App Store back in September.

Of course, Amazon has long been interested in voice. For years, Kindles have shipped with text-to-speech support, an accessibility feature which has gotten Amazon in trouble with publishers who felt that it stomped all over audio book sales. In addition, Amazon has increasingly moved away from text entry as a feature on their Kindle line-up, going as far as to drop the physical keyboard from the latest generation of e-readers.

Amazon’s purchase of Yap falls in line with many of Amazon’s plans for its Lab126 skunkworks group, which has been picking up smaller companies to integrate technology into the Kindle line-up that can’t be challenged by competitors’ patents. For example, Amazon bought Touchco in early 2010, thus picking up a form of multi-touch for the Kindle Fire that isn’t vulnerable to Apple patent attacks.

In addition, a Siri-like service makes perfect sense for Amazon given the Seattle online retailing giant’s massive cloud backend. Amazon has the server power to crunch voice and spit out smart results, all they need is the talent to incorporate it (which they now have) and a deal with a company like WolframAlpha to power it.

With their purchase of Yap, there’s no question that a future Kindle Fire will get Siri-like abilities. It’s just a question of ‘when’ and whether Amazon will be able to beat Google to market with the service.