Unfortunately, this has not yet happened, and while Apple's current voice command features do work very nicely, they're quite limited in what they actually let you do by voice.
This is in stark contrast to Google's Android OS, which has voice dictation and voice commands baked right in, even letting you speak navigation destinations for use with Google's own Maps Navigation software.
Given pre-WWDC rumours that enhanced voice features would make an appearance at the WWDC event, it's thus somewhat surprising to see that they made no appearance whatsoever, although the same rumour-meisters now seem to suggest that it's because Apple is keeping it for the next iPhone launch, whether that be the iPhone 4S, the iPhone 5 or the iPhone something else.
Any mention of Nuance was also missing, with Nuance providing the actual voice-to-text transcription technology, although TechCrunch, which has more info on this story, intriguingly points out that Nuance's 'Chief Mobile Technology Architect' was in the WWDC keynote audience.
Ultimately, it's clear that Apple announces what it wants to announce when it wants to announce it, unless one of its staff members 'accidentally' loses a voice-controlled iPhone in a bar somewhere, and seeing as improved voice command is a much-desired feature, it just makes sense to announce it later, such as with a new iPhone, if that feature isn't ready yet.
The feature might not yet be ready due to ongoing negotiations with Nuance, it might not be ready because it somehow dramatically improves on or simplifies what is offered by the competition (not that speaking into a microphone is that difficult) or because Apple just wants to be Apple and keep some of its cards close to its chest, as it surveys the fallout and reaction from WWDC thus far.
There's also the inevitable news that Apple's new iOS has been jailbroken already, as seen from iPhone Dev Team member 'MuscleNerd's' tweet.
However, just because a beta version of iOS 5 has been jailbroken does not mean that the final version will be so easy to crack open, especially if Apple introduces yet more hardware locks into whatever it is cooking up for the next iPhone release.
Thus, the world continues turning, the word will continue being spoken (and transcribed, even if only through Dragon Dictate on iDevices for now), and the cat and mouse game between Apple and the jailhouse hacktivists continues rockin'.