Apple confirmed today ( and they even gave an impressive demo of Siri today, during the media event ), that they will bring Siri voice control to the iPhone.
Siri will let you speak to perform tasks like getting directions, setting an alarm, ask for weather forecast, making a calendar appointment, search Wikipedia and WolframAlpha, supports dictations etc. Siri describes himself/herself as a ‘humble personal assistant’ and will work with built-in apps over 3G and WiFi.
Siri will work in English ( US, UK and Australian ), German and French. It will start in beta-phase, but Apple says it ‘gets better’ as it learns your voice.
Apparently Siri will be available just on the iPhone 4S. Was unclear if it will be supported on the iPhone 4 or 3GS.