The Time Machine
Back! Back! Back! Back to a time of low-tech thrillers!
Cellphones have destroyed the horror genre. In real life, if a bunch of teenagers found themselves stranded in some sub-podunk village with a maniac killer running around, they could just call (or SMS) for help, direction, movie listings, etc.
Cellphones have also killed the payphones, privacy, and dolphins. They're bad news. And you're bad for having one.