I might add that although I carry a cell phone I never turn it on except to use it. As I mentioned in a previous post I have used it to call the police when being harassed by motorists and it was quite effective in that application. I used it to report a brush fire once and I think, since I was the first to report it, I probably mitigated the property damage quite a bit. I also once called in an obviously DUI driver that was having trouble negotiating the parking lot he was in. The cops grabbed him before he made it out onto the road. So, are mobile phones essential? no. Have I used it a few times where the situation would have been worse if I didn't have it? - you bet. For the $10 a year I pay for it I think it is worth it.

BTW, I think this thread really would be a better fit over at Living Car Free since the OP's intent seems to be for making a case for doing without. He will find many over their who will sympathize with the do without attitude.