I first read this when it came out in 2006, and I thought then, and maintain now, that the conceit, as presented in the title of the book and the promotional material for the book is dumb as hell, but the book itself, is smarter. “Your number is up!” the book cover screams! But the book itself, where, one afternoon some kind of “pulse” goes through cell phones causing each user who happens to be on a call at the moment, and anyone making a call thereafter to revert to some kind of atavistic human id mostly resulting in extreme violence of some kind: think zombies but also Bird Box. Our protagonist just so happens to be one of those guys who doesn’t have a cell phone in 2006, sees what’s going around him, and gets to safety with a couple of non-insane people from there.
On the road, they notice that the “zombies” are not just acting irrational but have adopted some kind of flock mentality or hive mind and are acting in accordance with some set of impulses not entirely knowable to outsider viewers. The plucky band looks for answers.
So the book is basically “Mini-The Stand” or in some ways lays out the groundwork for big chunks of the Walking Dead. But unlike a lot of those movies, the monsters ARE the monsters, and so this book is a streamlined version of those stories, with no evil humans (for the most part) to contend with. It still has plenty of annoyingly “pointed” commentary about cell phone usage and the like, but for the most part it’s a pretty solid rendering of human behavior in an unprecedented crisis.