Incidently I have over the years serviced lifts on what we called caretaker maintenance ie 4 times a year. We shut the lifts down, when completed. Even with that program phones were required, however I did hear of lifts shut down and essentially not serviced and kept up to date ie phones as well. However, when they were turned on again, they had to be brought up to date again, including phones, but also potentially other systems that were ok, whilst continuous use was happening. Not the best way in the long run, and you still would be liable in the case of someone happened to get stuck in it. I wouldn't recommend this way at all.