Cellular

Who are you? How did you get involved?
I just answered my phone.

Cellular is a 2004 film starring Jason Statham, Kim Basinger, William H. Macy and Chris Evans.

Middle school biology teacher Jessica Martin (Basinger) is kidnapped by Ethan (Statham), who is after her family for unexplained reasons. He and his gang lock her in an attic where he smashes the landline phone to avoid her calling out. She manages to jury rig the phone to be able to dial out again-- but the rotary dial is destroyed, she can only tap out the numbers. Dialing blindly, she manages to connect with Ryan's (Evans) cellular phone. Ryan is an irresponsible commitment phobic trying to hook back up with an ex-girlfriend, he refuses to believe Jessica and thinks she's prank calling, but she pleads that if he hangs up she may not be able to reach anyone else at all. So he decides to believe her and take his phone to the police where they can decide if she's serious or not. Midway up the precinct's stairwell, he starts losing reception just as Ethan returns and starts hurting Jessica to find out where "it" is and where her husband is, and tells her he's going after her son. With no question of her and her son being in danger, Ryan undertakes a harrowing chase across the city to try to protect her son, discover why (and where) she's been kidnapped and avoid dying along the way.

All while avoiding losing cell signal and battery power.

Along the way, Sgt. Mooney starts unraveling the trail of chaos left in Ethan and Ryan's wake, while investigating Jessica's kidnapping. He's about to retire, so...

There's a 2008 Hong Kong Remake called Connected, directed by Benny Chan. It, too, is worth checking out.

Tropes used in Cellular include:

Action Survivor: Ryan and Jessica. The former for managing to run, drive and dive across L.A. and live, the latter for killing a man with Biology!, choking another, and saving her family in the process.
Apologetic Attacker: Twice. The first time Ryan apologized for holding up a Cell Phone store with a gun to steal a phone charger... though he did pay for it. Later mixed with Explaining Your Power to the Enemy. Jessica apologizes to a thug after killing him through a single cut below on his arm. See Chekhov's Skill below.
Bald of Evil: Ethan.
Can You Hear Me Now?: Subverted, the movie uses the facts of cell phone use realistically (though of course dramatically.)
Chekhov's Skill: Jessica is a biology teacher, which means she knows exactly which artery to cut to kill a man in less than a minute.

Jessica: Tenth grade biology. Brachial artery... pumps 30 liters of blood a minute. There's only five in the human body. I'm sorry.

Confiscated Phone: When his battery is abut to die, Ryan buys a cell phone charger at gunpoint in order to obtain instant service.
Creative Closing Credits: Edited into every cellphone screen that appeared in the movie.
Creator Cameo: Producer Dean Deviln is a cab driver. Also a bigwig of New Line Cinema.
Dirty Cop: The people behind the kidnapping.
Distress Call: Jessica's phone call.
The Everyman: Ryan is an ordinary kid who Jason Statham's villain coldly rebukes "Even the bitch has more fight than you" as he mercilessly administers him a No-Holds-Barred Beatdown.
Female Gaze: When we first see Ryan he doesn't have a shirt on and my, does he look fine without one.
Foreshadowing: Early in the movie, Ryan tries to convince his ex-girlfriend he cares about her pet cause (Save The Bay). He sees an obscured sign and tells her he's there to "save the day".
Heroic Bystander Ryan is just a guy on the street who gets a phone call, but once he realizes it's not a prank he goes to extraordinary lengths to help Jessica.
Honor Before Reason: Lampshaded by the fact that the Chinese character on Ryan's arm is read as "honor" and/or "loyalty", the defining traits of this otherwise completely ordinary boy.
Hypocritical Humour: Ryan while driving yells for a girl to get off her cell phone and concentrate on the road. All the while he's talking to Jessica.

"Get off your cell phone! Concentrate on the road! IDIOT! *to Jessica* You still there?!"

Improbable Aiming Skills/Imperial Stormtrooper Marksmanship Academy: Officer Mooney ALWAYS gets the shot, the Bad Guys are lucky to graze his neck. Though it is a bit subverted as the Bad Guys are always firing on guys who have cover and/or are moving and Mooney fires several shots and usually only gets one, but he is waiting for the right shot instead firing blindly, so he has time to aim and plan.
Insistent Terminology: "It's a day spa!"
Minor Crime Reveals Major Plot
Oh Crap: The look on Ryan's face when the oil trucker slams into Ryan's stolen security car is priceless.
Ooh, Me Accent's Slipping: Jason Statham's native British accent fades in and out during his dialogue throughout the movie.
Playing Against Type: Jason Statham as Ethan, the chief villainactually the Dragon-in-Chief.
Precision F-Strike: "It's a day spa, you fuck!"
Product Placement: Well, the whole plot revolves around a cell phone, whose brand can be clearly seen in one or another scene.
Recycled Script: Had Phone Booth not spent 40 years in Development Hell (and two and a half years on the shelf after being completed), this film probably would have never happened.
Retirony: It's Mooney's last day on the job, and he lives through the end! Subverted Trope, ahoy!
- Also subverted in that despite his age he still knocks the stuffing out of one of the criminals.
Ripped from the Headlines: Sort of. The film of course doesn't brand it self as being true, unlike some other movies but some ideas were inspired by the infamous Rampart Scandals done by the LAPD in the early 1990s.
Running Gag: Everyone keeps on calling Mooney's post career business a beauty salon. The final time ends in the Precision F-Strike mentioned above.
Spiritual Successor: To Phone Booth, also written by Larry Cohen. That film's intentionally limited setting and claustrophobia was inverted by this film's wide-ranging action and motion.
Shout-Out: The The Lord of the Rings backpack a nod to the Lord of the Rings movies also released by New Line Cinema.
This Is for Emphasis, Bitch: The thug that Jessica kills manages to do nothing but choke up until his last moments when he looks up and chokes out, "... bitch".
Title Drop: The name of the cellphone store Ryan "robs" is named Cellular.
Who Names Their Kid "Dude"?: Jessica's son is named Ricky Martin. She explains he's not named after the singer.
Willing Suspension of Disbelief: We're just going to pretend that a middle school biology teacher is capable of taking a phone smashed to pieces with a sledgehammer and repairing it into working order using no tools but her bare hands. It makes the movie so much easier.
- In all fairness, a sledgehammer is a very poor choice of tool for destroying wires. And she was clearly lucky to get anyone at all.
  - The Chinese remake changes the woman's job to some sort of tech-whiz engineer, making it more believable.
  - But then how does a tech-whiz engineer know about the brachial artery?!
  - Wikipedia?