Read the book!
I watched the film and am nearly finished with the book.
I implore you to read the book as is it much better. Helped me understand far more. Also spends much more time on the "telepathy" and flocking nature of the "phone crazies"
I didn't mind the film as much as some but felt it would've played better as a limited/mini series on TV maybe? You certainly could keep Cusack as the main character.
But it would need to stick closer to the book than the film did. I think that is why the film doesn't quite cut it.
You cannot fix faith, River. Faith fixes you. - Shepherd Book, Firefly