According to sources that contacted Ars iPhone firmware 3.0 will have voice control and feedback in addition to the tons of other new features previously reported. Codenamed "Jibbler" the iPhone voice system will include both voice recognition to allow you to control the iPhone by speaking and voice synthesis similar to the latest iPod Shuffle which can "read" track titles etc to you.
"Jibbler" will probably be an enhancement to the iPhone's spingboard somehow -- the details aren't clear. It also reportedly supports spotlight. Support for the Jibbler report are references to classes in the iPhone firmware including VSSpeechSynthesizer, VSRecognitionSession, SBVoiceControlDisableHandlerActions, SBSensitiveJibblerEnabled