Take American Graffiti. If that film had been set today instead of 1962, it wouldn't have made any sense at all—and not because kids don't hang out at sock hops and in diners anymore. Richard Dreyfuss would never have spent the night split between his ex-girlfriend and a local gang if he had been able to call all his friends, and he definitely wouldn't have asked Wolfman Jack to read his cell phone number over the radio airwaves in an attempt to connect with a hot blonde woman, allowing all of Modesto to prank call him. He would have never received a call from said love interest in a pay phone, because pay phones are impossible to find these days.
Sixteen Candles would not have been a charming love story about a mismatched couple but rather a harrowing tale of teen bullying. If texting had existed on Molly Ringwald's sweet sixteen, half the school would have images of her underwear and sex quiz on their cell phone faster than you can say "Long Duk Dong." But at least she probably would have had a surprise party: Thanks to Facebook, her parents likely would have been reminded of her birthday and planned emergency festivities. Hijinks never would have ensued.
Can't Hardly Wait, one of the last pre-cellular age One Crazy Night movies, wasn't terribly plausible when it came out in 1998, but it would have been utterly exasperating if it had been released a decade later. A teenage Asher Roth-type would not have lost his virginity, because there is no way he would have spent a whole night locked in a bathroom with the goth-ish misfit had either of them been able to call their friends to break them out. The nerdy valedictorian would have avoided being the subject of compromising Polaroids and going to jail if he had been able to text his minions and abort a revenge attempt on the popular jock (meanwhile, the screenwriters could have avoided a lame and sort of obvious gay joke, so there's that). Protagonist Ethan Embry would not have found himself at a gas station pay phone, having a revelatory conversation with an exotic dancer dressed as an angel. He also might have considered pouring out his heart to Jennifer Love Hewitt via e-mail instead of trying to hand-deliver a love letter to her at a crowded party.
The few One Crazy Night movies produced this decade tend to be far less straightforward than their predecessors. Much like horror movies use dead zones to explain why the pursued aren't calling the cops already, comedies and dramas of this ilk now mainly rely on people getting black-out drunk and going on quest to explain why they get in crazy situations where they can't communicate with each other. The Hangover only works because all of the characters have rohypnol-induced amnesia. In Harold & Kumar Go to White Castle, cell phones are beside the point when the leads are that stoned. Nick and Norah's Infinite Playlist features only one truly wasted character—and the movie suffers because of it, since everyone else just seems incompetent.