For those of us who have them, the answer would be "Indispensible." The majority of the American population over the age of 16 (and I'm afraid it's probably even younger than that) has a personal cell phone. And really, they are marvelous inventions that most of the time make our lives much, much easier. Except, of course, when one is taking a name and gets interupted by a vibrating phone.
However I recently went two weeks without a phone due to loosing my old one and I was forced to really face the reality of how much we depend on our phones. I actually managed to survive just fine, but I found myself feeling quite amused and slightly annoyed whenever someone said "but it's dangerous to drive without a cell phone!" or something along those lines.
Because, of course, it's only in the last decade that cell phones have been really common. For thousands of years before that people went on great journeys and adventures without cell phones and managed to survive just fine! I mean, Christopher Columbus discovered America without a cell phone. The Apostle Paul went on all of his missionary journeys without a cell phone. Father Abraham traveled from Ur to Canaan without a cell phone. Those were all much more dangerous journeys than driving fifteen minutes to visit one's grandparents - even if it IS snowing outside.
Sure, all those journeys would probably have been easier with cell phones, but the point is - they managed without them. So it's really not something worth fussing or worrying about if you have to go two weeks without a cell phone. I mean, you still have pay phones and house phones and internet and, if all else fails, smoke signals.