You don't need a minicomputer to call 911. You don't need a minicomputer to text your wife that you're running late. You might be surprised what a smartphone is useful for though.
I've had a smartphone for about six months now, and before that I didn't really think I needed one. Now I know I don't need one, and right now I don't even have cell service, but I have found a number of uses for it anyway. I've used mine as a flashlight, a level, as a compass, and to check my pulse. They make you wish you had a real camera, thus fueling the economy, and they will do in a pinch if you need photographic evidence of something. It makes a great guitar or instrument tuner. It will translate text on a billboard. It saves paper for grocery lists. And there are about a half million things that any networked, powerful computing device would be useful for: games, alarm clock, programming, et cetera.
However, I think I have an even better example. I came home for the holidays to Valdez, Alaska in 2011. As undoubtedly nobody knows, Valdez is by far the snowiest city in America with about 325 inches (8.25 m) of snow in a given year. That year was an extraordinary year for snow. By late January 350 inches lay on the ground, and this in a place where snow showers in May were not unheard of. Boats sank. Buildings collapsed. Everyone who could was shoveling. After the second time I cleared our roof the snow pile reached the second-story windows on every side of the house. This became a slight problem at about the same time when the heating fuel started to get low — the (chest-high) fill pipe for the house was now buried three times its height in snow. You'd think that these sort of permanent-house-features would be easier to find in this sort of situation. I spent about three days digging for the damn thing, but then remembered something a friend had mentioned: the magnetometers in smartphones can be used as metal detectors. I tromped in, borrowed my mom's cell, and found the pipe almost immediately. I'd come within a few inches of it, but then been digging in the wrong direction. It wasn't exactly a life or death situation, but it was pretty dire, and it was pretty much the only tool available that could have helped in that situation.
I get your point that smartphones enable some people to be rather conspicuously vapid, but I'm not sure that they wouldn't be just as irritating with some other toy. I do think it's wrong to disdain the tool because of the users. I'm glad you don't need one. I'm glad I had one when I needed it. I'm pretty okay with having one now, even if I don't use it much. Most especially I'm glad that my mom doesn't live in a place that gets thirty feet of snow in a year. However, if you do happen to visit that terrible place, I highly suggest you bring a smartphone. You never know when it might come in handy.