On another forum some people are claiming they have downloaded a GPS app onto their iPhone that works great, able to download maps, etc. But to use it as a functioning GPS unit, doesn't it require to have cell service as well? There are some hunters planning on going out west to hunt and pan to just use a GPS app instead of getting an actual functioning GPS unit. I would think they're going to be in for a surprise if they get somewhere in the mountains with no cell service. Am I correct in thinking this or not? Thanks.