A quick thought about horror writing…
Personally, I find horror written in epistolary form to be especially scary, as it is particularly good at producing a feeling of trepidation and anxiety. It does this by offering an incomplete first-person viewpoint with no narrative explanation — one source of uncertainty — and also forces the reader into the position of the receiving party, the hidden participant in the relationship, worried for the writer, which generates another source of uncertainty and anxiousness. If the story is represented by the writings of more than one character, the reader may end up with more information than the protagonist, but due to the feeling of relationship with him or her, the reader’s fear is heightened rather than lessened by this, due to the impulse to protect — by a subconscious desire to get this vital information to the protagonist — even while consciously knowing that this is impossible. A fantastic example of this: Dracula by Bram Stoker. Also, a story I heard on the more-than-worthy-of-subscription podcast, Pseudopod, “The Western Front” by Patrick Samphire.
No post here would be complete without an obnoxious aside. Have there been any serious (meaning not CollegeHumor.com posts) stories or novels written in phone conversation? IRC? SMS? Would they still be considered “epistolary”? Or is there/should there be a new word for them?