Disembodied, but, Oh, What a Voice She sounds like the girl next door - young, friendly, eager. For Theodore Twombly (Joaquin Phoenix), the poetically melancholic hero in "Her," Spike Jonze's exquisite new movie, that voice (Scarlett Johansson) is a lifeline to the world, which he has loosened his hold on since separating from his wife. The voice brightly greets him in the morning and, with a sexy huskiness, bids him good night in the evening. The voice organizes his files, gets him out of the house and, unlike some multitasking females, doesn't complain about juggling her many roles as his assistant, comfort, turn-on, helpmate and savior - which makes her an ideal companion even if she's also just software. At once a brilliant conceptual gag and a deeply sincere romance, "Her" is the unlikely yet completely plausible love story about a man, who sometimes resembles a machine, and an operating system, who very much suggests a living woman. It's set, somehow of course, in Los Angeles, that city of plastic fears and dreams, in an unspecified time in the future. The machines haven't risen, as they have in dystopian tales like "The Terminator" series, but instead have been folded into everyday life. Theodore learns about the operating system from an advertisement and is soon running it on his home computer and phone. Before long, he and the software, which calls itself Samantha, are exchanging pleasantries, playing the roles of strangers fated to become lovers. It's a perfect tale for Mr. Jonze, a fabulist whose sense of the absurd informs his more broadly comic endeavors (notably his work on the "Jackass" movies, including "Bad Grandpa") and the straighter if still kinked art-house films he's directed, like "Being John Malkovich" and "Adaptation." If it has taken time for the depth of Mr. Jonze's talents to be recognized, it's partly because of all the attention bestowed on Charlie Kaufman's scripts for "Adaptation" and "John Malkovich," which announce their auteurist aspirations on the page. It's perhaps unsurprising that Mr. Jonze's third feature, "Where the Wild Things Are," an emotionally delicate live-action adaptation of that Maurice Sendak book, was a visual knockout with a minimalist story and relatively little dialogue. Written by Mr. Jonze, "Her" features plenty of talk and comparably little action partly because it's a neo-classic boy-meets-operating-system romance and only one of them has a body. This is a minor setback as far as the characters are concerned, although only Samantha frets about it. If this profound existential difference doesn't worry Theodore, it's because isolation is his default state. That's both because of his own life-historical events, including his separation from his wife, Catherine (Rooney Mara), and because everyone around him seems more plugged in to their machines than to other people. He has one friend, Amy (Amy Adams), who lives nearby, and talks to only one colleague (Chris Pratt) in the office where he spends his days writing intimate letters for other people. In "Her," everything is simultaneously familiar and unfamiliar, like all the voice- and gesture-activated software that Theodore uses at work and at play, as if his era had caught up to today's prototypes. Mr. Jonze and his superb production designer, K. K. Barrett, haven't reinvented the world, only modestly embellished ours, as with their reimagining of Los Angeles (a role played by that city and Shanghai, with digital assistance). The city still sprawls to near-infinity, but it's now as vertical as Manhattan, and everyone travels by train, not car. The trains are a low-key, witty touch (and true science fiction), but they also let you see early on how lonely Theodore is even in a crowd. Samantha saves him from solitude, drawing him out of himself and then into life itself. The role was initially voiced by the British actor Samantha Morton, who, after the movie was shot, was replaced by Ms. Johansson and whose casting feels inevitable. Her voice isn't an especially melodious instrument, but it's a surprisingly expressive one (as Woody Allen has figured out) that slides from squeaky girlishness to a smoky womanliness suggestive of late nights and whiskeys. It's crucial that each time you hear Ms. Johansson in "Her," you can't help but flash on her lush physicality, too, which helps fill in Samantha and give this ghostlike presence a vibrant, palpable form, something that would have been trickier to pull off with a lesser-known performer. "Her" is even harder to imagine without Mr. Phoenix, an actor who excels at exquisite isolation. Wearing a tidy mustache and horn-rimmed glasses that temper his good looks with a hint of Groucho Marx comedy, his Theodore - shoulders slumped and pants unflatteringly hitched up - presents a harmless, defeated picture. At his most memorable, Mr. Phoenix plays wounded, stunted souls whose agonies are expressed almost reluctantly in halting words and somatic contortions, as in his brutal performance in Paul Thomas Anderson's "The Master." His work in "Her" is quieter, more openly vulnerable than in "The Master," yet, surprisingly, as powerful because, once again, it feels as if his character's solitude had been drawn from some deep, unarticulated place in Mr. Phoenix's own being. There are times when "Her" has the quality of a private dispatch, like a secret Mr. Jonze is whispering in your ear. Part of the pleasure of the movie is its modest scale, its hushed beauty and the deliberate ordinariness of its story. In contrast to the hard shininess of so many science-fiction movies, "Her" looks muted, approachable and vividly tactile, from Theodore's wide-open face to the diffused lighting and the ravishingly lovely sherbet palette splashed with mellow yellows, tranquil tangerines and coral pinks. This is a movie you want to reach out and caress, about a man who, like everyone else around him in this near future, has retreated from other people into a machine world. In "Her," the great question isn't whether machines can think, but whether human beings can still feel. "Her" is rated R (Under 17 requires accompanying parent or adult guardian). Some voiced sex and fantasies. Her Opens on Wednesday in New York, Los Angeles and Toronto. Written and directed by Spike Jonze; director of photography, Hoyte van Hoytema; edited by Eric Zumbrunnen and Jeff Buchanan; music by Arcade Fire and Owen Pallett; production design by K. K. Barrett; costumes by Casey Storm; produced by Mr. Jonze, Megan Ellison, Vincent Landay and Daniel Lupi; released by Warner Bros. Pictures. Running time: 2 hours 5 minutes. WITH: Joaquin Phoenix (Theodore), Scarlett Johansson (Samantha), Amy Adams (Amy), Rooney Mara (Catherine), Chris Pratt (Paul) and Olivia Wilde (Blind Date).