Apple is working hard on Speech to Text integration in latest iOS 5 releases and now it seems that this is going to happen in the final release of iOS 5 which is currently in Betas for developers only.
According to 9to5Mac Nuance Speech to Text is already built in iOS 5 SDKs and it can be enabled from Springboard by turning the Dictation Mode on.
By enabling this Dictation mode a button will appear near keyboard which will allow Speech input from user and later convert it to Text. This feature will be available for all apps installed in iPhone, iPad or iPod Touch having iOS 5 final built. On enabling this feature a microphone will appear on keyboard as show in snap below,
On clicking that Microphone the Dictation mode will be turned on and everything you speak will be converted into text and entered in to the respective text box your are currently on.
Currently this functionality is in Beta testing and may appear differently in final release of iOS 5. Moreover it has been learned that Apple is planning to deploy this just on their iPhone and iPod Touch same as their Notification center Widget and Voice Control whereas iPad would not be included in Speech to Text functionality as the keyboard on iPad is already very handy for faster typing.