Apple has acquired virtual personal assistant company Siri, according to an FTC filing asking the agency to let the deal close before the end of a statutory waiting period.

Siri’s technology is designed to handle a back-and-forth conversation with software that acts as a virtual personal assistant.  The technology is embedded with contextual awareness about a user’s individual preferences and context, such as place, time and history.

The Siri app is available as a free download from Apple’s App Store for the iPhone 3GS and the iPod Touch. The app works only in the United States.

According to Siri’s website, the app will “soon” run on the iPhone 3G and other mobile platforms. It is unclear whether Apple’s acquisition of the company will affect Siri’s plans to expand to other operating systems.

Neither Siri nor Apple replied to requests for comment by press time.

The acquisition of Siri marks Apple’s second purchase this week. On Tuesday, The New York Times confirmed that Apple had purchased Intrinsity, the rumored manufacturer behind iPad’s A4 chip.

The chip is believed to reach 1000 MHz, making it 350 MHz faster than most chips currently on the market.