I understand that when using spoken dialogue you would write it as "Hello Mary, how are you?" However, how would you define character written conversation or letters? For example, would I write it out using italics to define a non-verbal medium of communication? David picked up his phone and began typing a message. Hello Mary, how are you? Or would I alter the font style or size to differentiate written communication? David picked up his phone and began typing a message. Hello Mary, how are you? I have seen it in various styles, although I personally read italics as an internal character thought rather than an external expression. What are your thoughts?
You could just write it as David picked up his phone and began typing a message: hello Mary, how are you? It depends what you are planning on doing with your story/book. I have heard that publishers and agents don't like people using different fonts (italics are ok) so if you are looking to publish your work the traditional route don't use a different font. But, on the other hand, if you are self-publishing or publishing it on a blog, or whatever, the second option could work nicely.
You quote it like any other form of dialogue. It is still a communication. For letters, a block quote is often the best choice. A block quote is an indented block of text without quotation marks. Italics are NOT correct. See He said, she said - Mechanics of Dialogue
ditto that... to repeat, it's still 'dialog' and a 'quote' and must therefore be in " " if not inserted as a block indent.. and not italics or any different font... what you have seen are the printed books, not a submitted ms... and what you must submit is a properly formatted ms, not what you wish to see in the printed book, if you want it to be read and taken seriously by agents and publshers...
Thank you all, thats cleared that one up. I have revised where i have character written dialogue now, pending an answer on this thread. Luckily i am not too far through yet.