When Apple came out with the IPhone one of the features that everyone was amazed with was the typing feature on it. Since the phone had a touch screen Apple had the ability to innovate the way people texted on the IPhone. It took a while for me to get used to at first but now it has become as easy as typing on my computer. Another feature for texting on the IPhone is the history of your messages to different people, they have it set up as a chat log.
The main metaphor here would be a typewriter or a keyboard. However, since you have to do most of your typing with two fingers it kind of reminds me of how people used to use two fingers to type on a type writer.
Concepts of texting on the IPhone include, dictionary, history of the texts, mass texting.
You get to keep track of what you were saying to someone and not have a hard time looking for old texts to particular people.
The layout of the keyboard is exactly the same as computer keyboards. You can look at all the texts to one particular person.