According to developers who are beta testing the next generation of iPhone operating system software, there's a built in feature called Jibbler that allows applications to take advantage of voice recognition technology.
While it's mainly speculation at present (why isn't that a surprise), ArsTechnica came across references to classes and methods called VSSpeechSynthesizer, VSRecognitionSession, SBVoiceControlDisableHandlerActions, SBSensitiveJibblerEnabled, and SBVoiceControlSoundCompletion.
SB means SpringBoard (an existing iPhone application) and VS could well be Voice Services.
I've long wanted decent voice recognition software on the Mac, so to get it on the iPhone instead would be great, presuming it does rather better than Mac OS X's current Speech application.
(Via PC Mag)