Consider the question. Coordinates: 47 00 01" N 109 45 04" W / 47.00028 N 109.75111 W / 47.00028;-109.75111 (State of Montana) Area code 406 is the telephone area code covering the entire state of Montana. It has been Montana's area code since area codes were created in 1947.

Answer this question based on the passage: where is area code 406 located in usa?
What is the step-by-step reasoning process to arrive at the answer: the entire state of Montana?
The relevant information is: Coordinates: 47 00 01" N 109 45 04" W / 47.00028 N 109.75111 W / 47.00028;-109.75111 (State of Montana) Area code 406 is the telephone area code covering the entire state of Montana.