When it comes to using your voice to dictate your content to a computer rather than typing, there are a bunch of apps out there already. Dragon Naturally Speaking is one such voice instead of typing software package. A company called Avatron has invented a new app for the iPhone that harnesses Siri to enter text.
The app is called Air Dictate and Avatron developed some sort of method to harness Siri's voice capturing abilities to transfer the text that Siri pieces together from your speech over to a Mac. The Mac computer needs to be on OS X 10.6.8 or higher and running the Mac portion of the Air Dictate Receiver App.
Once all the software is set up, you can then just talk to Siri for email, Word, Pages and all the other software that needs text input. I can see this being an interesting way to perform dictation for those that already have the iPhone and want to use it rather than a microphone.