On the iPad 3 or later or an iPad mini, you can dictate messages that will then be typed out. To do this, tap the microphone key (if the key isn’t visible enable Siri from the Settings app, then General, then Siri) next to the space bar and start speaking. Once finished, just tap Done.
To include punctuation, just speak it. For example, for the sentence “Hey, how are you today?” you would say, “Hey comma how are you today question mark.” You can even add paragraphs by saying, “new paragraph.”