When I was on the Isle of Skye, I was very surprised to see such phone boxes in very remote places. A phone box next to the street, but no houses visible. I wondered who is supposed to use them? Here, the locations for public phone boxes are chosen on the base of possible revenue or the importance of a certain location (i.e. train station, airport, …). So, you won’t find any in remote places. My advice when coming here: have your cell phone available when going to remote places or hope for other people to find you in case you have an accident or need help for another reason.