Question: As his wife, why does Jessica address Brody by his last name instead of his first name?
Question: One thing I do not understand is this... "if" the souls of the deceased (that die within the walls of "Murder House") are trapped there for eternity then how does the maid get to go see her mother (obviously off premises) and Tate get to meet up with Dr. Harmon for coffee for his appointment?
Chosen answer: Because on Halloween, the souls of The Dead are said to roam the Earth. That includes those souls that are trapped within the walls of the "Murder House".
Question: Why did the cord on the wall phone in the police station change from straight in the early episodes to coiled later?
Answer: There's probably no particular reason. Sets and props on long-running TV shows often change as needed and for various reasons throughout a series run.
As long as such changes aren't an obvious continuity mistake (e.g. changing multiple times during a day), one can just assume the change happened in-universe as well. Things do get broken or updated occasionally. It adds a bit of realism, in my opinion.
Chosen answer: Everyone else calls him Brody or Sgt. Brody, and it probably became habit to her.
The_Iceman
Can't get the source but I read that even the Producer responded to that. Stating that it was common practise for a military wife living in a military complex as everybody refers to their husband by their last name.