iPhone 4S Siri is the Personal Assistant for you which can perform various tasks which also includes creating and updating notes.
Also Read: List Of Siri Voice Commands In iPhone 4S
Dave Caolo of 52 Tigers how to create a new note and update using Siri:
To create a new note, tell Siri, “Create a new note,” “Make a new note” or something similar. You can give a note a title at the same time, for instance, “Make a new note packing list” or “Create a new note places to visit.” That becomes the first line of the note.
Updating note in Siri is also very simple as you just need to remember name of the note which you want to update or add and instruct Siri to add or update that note using Voice command.
One of the drawback of using Siri to create or update note is that you can neither delete nor share the note via email.