Even in the mountains you should be able to get a GPS signal; just climb until you do. Regarding the phone bit though, I don't get a signal in the woods even here in flat Florida (I've said before, if you get a signal, you ain't far enough away from civilization) I can partly understand people wanting to let family know they arrived safely, but I refuse to submit to a leash. For those that want or need a smart phone (or even an older dumb cell phone) there appears to be a fair few good options to power them already and I expect battery technology to improve still more. I also expect more and more folks are gonna want to take them just for the sake of taking them. If we base everything on "need" alone then we wouldn't be going into the woods or the mountains anyway; we go for fun. With that in mind, if your phone and the associated apps and devices are "fun" for you why wouldn't you take them?