Apple appears to have acquired Siri, a well-funded and promising startup that built a personal assistant application for the iPhone.

The deal was revealed in a filing with the Federal Trade Commission (to read the filing, download the PDF for April 27), which was then tweeted by blogger Robert Scoble. I’ve emailed Siri, but the company has not confirmed or commented on the news. (Chief executive Dag Kittlaus is pictured above, center, with cofounders Tom Gruber and Adam Cheyer.)

Here’s how I described Siri when the app launched back in February:

Basically, you tell Siri what you want to do, and it connects you to the right online service to make it happen.

For example, you could say, “I want to make reservations for two at a cheap Italian restaurant tomorrow night,” and Siri will find appropriate restaurants. You can also ask more general questions, like, “What’s going on tonight?” which will get you a list of nearby event listings. In both cases, the app doesn’t just supply information, but also allows you to take action — you can make a reservation at the restaurant of your choice, or you can buy a ticket for a concert.

The concept wasn’t new, but Siri’s execution was impressive — the technology (licensed from Nuance) for translating verbal queries into text worked pretty smoothly, and Siri itself did a good job of translating casual, vague spoken requests into specific, actionable commands. The main limitation was the fact that it only focused on a few areas, including restaurants, movies, events, local businesses, taxis, and weather. For that reason, even though I always mentioned the app as an impressive technology, I didn’t actually use it as often as I thought, and I’ve heard anecdotally that others had the same experience. As Siri (or whatever Siri becomes) adds more features, that could change.

As a startup, Siri’s business model involved taking a cut of the money earned from all the transactions it facilitated. Apple might also want to make money that way, but the real value probably lies in enhancing the iPhone by including Siri as a built-in app. I wouldn’t be surprised if Apple includes a “Personal Assistant” app in an update of the iPhone operating system sometime soon. And if I were a startup trying to sell my own personal assistant app on the iPhone, I’d probably be worried.

The San Jose, Calif. company has raised $24 million from Menlo Ventures and Morgenthaler Ventures.

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