I had no business enjoying For A Good Time, Call . . . as much as I did. This featherheaded romantic comedy, built on the improbable and arguably offensive premise that a bright young woman’s surest path to financial success and personal actualization is a career in phone sex, is crude and derivative and only sporadically funny. For every burst of giggles, there’s an equal and opposite eye-roll or stretch of joke-free tedium.

But there was something about the buoyant spirit of this raunchy female-friendship comedy, directed by Jamie Travis and co-written by its star, Lauren Miller, and her former roommate Katie Anne Naylon, that won me over anyway.

Maybe it’s just that the two leads, played by Miller and the husky-voiced Angie Dickinson lookalike Ari Graynor, have such sweet, fizzy chemistry together. Miller’s character Lauren, a Type-A aspiring book editor in her 20s, must look for a new place to live when her arrogant boyfriend (James Wolk) dumps her for being “too boring.” At the urging of her meddlesome gay best friend Jesse (a rom-com stereotype, yes, but Justin Long plays him with such brio that the character emerges as a specific, endearing person), Lauren agrees to take a room in the rent-controlled Gramercy Park apartment of the blowsy, wisecracking Katie (Graynor), who’s inherited the place from her deceased grandmother but is having trouble holding on to it.

Lauren can’t figure out how Katie — a part-time manicurist who seems to lounge around in animal-print peignoirs for much of the day — makes enough money to pay her half of the rent. But the theatrical moaning issuing from Katie’s bedroom at the same time each night finally tips Lauren off: Her roommate is operating a phone-sex line, albeit erratically and unprofessionally. No promotional website? No dedicated landline?

When she’s turned down for a big job in publishing (the script is curiously nostalgic, or maybe just oblivious, when it comes to the state of that industry), Lauren pitches her roommate a deal: If she takes care of the business side and makes the phone-sex venture profitable, will Katie give her a break on the rent till the end of the summer?

From there, the film’s plot unfolds like a female-centric Risky Business. The girls acquire two old-fashioned fuchsia princess telephones and a dedicated number: 1-900-MMM-HMMM. Soon so many calls are rolling in that they have to hire a second phone-sex worker, a diminutive, baby-voiced woman with a gift for spewing creative filth (played to a T by the magnificently named Sugar Lyn Beard). Though she enjoys her role as business manager, Lauren starts to wonder whether she shouldn’t try being on the receiving end of the phone calls once in a while, and in a giddily filthy montage, Katie schools her in the art.

The director Kevin Smith and Miller’s real-life husband Seth Rogen call up the girls for some humiliating self-abuse sessions (“Back it up!” commands Smith as Graynor emits beeps like a truck going in reverse). As their business booms and their intimacy deepens, the roomies experience a burst of homosocial attraction that, refreshingly, is never played for voyeuristic audience appeal. In fact, when Rogen’s character, in the mood for a threesome, asks the two young women to describe one another, they turn him off by getting misty-eyed and sincere about their mutual esteem: “Her complexion is amazing.” “She’s the most honest person I’ve ever known.”

I should probably lodge an official objection to the movie’s intimations that phone-sex work is a swell option for floundering post-collegiate women, or that the regular caller on the other end of the line might just be a cute bespectacled indie dude (Mark Webber) who’s looking to fall in love. But I doubt many viewers, young females or not, will take this frothy comedy as a design for living. It’s a fantasy caper, a spiritual throwback to ‘80s comedies about empowerment through entrepreneurship, complete with a bouncy pop soundtrack and a witty candy-colored wardrobe designed by Maya Lieberman. (Katie’s snug denim jumpsuit, a throwback to the ‘70s vibe that Graynor’s style of beauty invokes, was a particularly great find.)

But it’s the movie’s affectionate portrait of female friendship, along with Miller and Graynor’s loose, playful performances, that make this whole imperfect souffle rise as high as it does. The final scene between the two friends is an extended dirty joke, an absurd crescendo of unintended double entendres that I won’t spoil except to say that I laughed out loud at virtually every goofy, filthy line.