Never underestimate the power of a voice.

The sleeper comedy “For a Good Time, Call,” in theaters nationwide, has perked interest in the world of phone sex.

It’s a long-time industry that is still quietly plugging away, despite the rise of Internet porn.

The film chronicles the adventures of two young women who launch a phone sex line together out of their New York City apartment. It’s not long before they’re rolling thousands of dollars.

But while real-life phone sex operators say the money is definitely good, they also caution that it doesn’t happen overnight.

Lynnea, 30, is a phone sex operator based outside Pittsburgh. She’s been in the industry for more than 10 years, and told Metro the notion of quick cash while working from home during her college years is what drew her to explore the profession.

In her first year, she made $20,000. Now, she said, she easily makes $160,000.

“It’s not quick money, you have to build your clientele,” Lynnea said. “It took about five years till I was rolling in money and I’m not making a million a month, but I’ve been able to purchase a home, I get new vehicles, I get exotic vacations, I can do all of that.”

Ruby, a phone sex operator who got into the industry as a stay-at-home mom, plays about 16 different female characters over the phone, from the hot and sexy Caitlin to the busty Roxanne.

She answers calls that are routed to her through her company’s dispatcher and gets paid 50 cents per minute. For her, the big money with phone sex — which she describes as narrated porn — comes from repeat clients who she can keep on the line. Her longest call lasted more than 10 hours.

“It’s probably not realistic to make 10-thousand in a month. You have to get publicity, you have to advertise,” said Ruby, who is originally from Queens but is now based in Florida. “If you can land what we call in the business a whale, you are going to do well, but those are few and far between.”

And, according to these PSOs, as phone sex operators call themselves, phone sex takes a lot more than a little dirty talk. It takes a certain personality to keep clients interested, leading them to call back again, they said.

And a PSO has to be willing to explore the deepest depths of sexuality. Lynnea refuses to talk about anything that is illegal in real life, like pedophilia or bestiality. But Ruby, a so-called “no-taboos” PSO, will discuss any fetish a client wants to talk about.

“Anything goes,” she said. “If you want to talk about reading a library book or you want to talk about getting your [expletive] cut off, that’s fine – I’m an actress.”

How secret are their secret lives?

While Lynnea admits that close friends and family know she works as a phone sex operator, she typically tells people in social settings that she is an operator for the Home Shopping Network. Though she currently has a long-term boyfriend who knows and accepts her profession, she said the topic wasn’t always easy to navigate.

“There have been guys I dated in the past that weren’t going to accept it, but that’s also someone I was not going to spend my life with, either,” she said. “I have had some that have gotten concerned as if I am cheating on them, but that’s not the case.”

Just a 9-to-5 job

Ruby, a single mom, started taking calls as a PSO from 9 p.m. to 6 a.m. in a room on the other side of the house from where her kids were sleeping. She told Metro once her son became an adult, she told him what she really does for a living and he supports her.

“I’m very up front with it, I’m not ashamed of what I do,” Ruby said. “This is my job, just like if I was a nurse or a teacher.”

A PSO’s kinkiest calls

Aside from fielding calls from drunk or mentally disturbed people (which is about 15 percent of the time, according to Ruby), PSOs encounter just about every sex fetish out there. While the majority of men who call are either looking to play out fantasies where they are dominated or experimenting with another man, Ruby and Lynnea said they’ve received plenty of requests that surprise even them.

“One of the ones that always sticks out is dryer boy,” Ruby said. “He wanted to make believe he was in the dryer and he was being tumbled around.”

Another man who calls Ruby likes to wear pantyhose and fantasize that she is shoving 1,000 worms down his stockings, she said.

“I always say I have heard everything and then I get something new,” she said. “I’ve had guys tell me they are at a morgue and are going to be playing with dead bodies.”

Lynnea, too, can attest to countless unusual requests.

“One of my more unique clients, his fantasy was the movie ‘Barbarella,'” Lynnea said. “[On the call] I meet him in a bar or I meet him at work, but he puts me in the orgasm machine and he just wants to listen to me moan.”

Ruby said one of the hot topics on her calls right now is “cuckholding” — when a man is “forced” to watch his wife or girlfriend have sex with another man. She said the two other most popular fantasies among her male callers are experimenting with another man or being dominated by a woman.

Is phone sex your calling?

Phone sex operators predict a rise in interest from women considering joining the profession following the release of “For a Good Time, Call.”

“Every time there is some type of media exposure, I got swamped with applications,” Lynnea said, adding that prospective PSOs have to brace themselves for disturbing calls.

“You are going to encounter every issue because you are talking to men nationwide,” she said. “You will encounter racists who want you to use racial slurs in your phone sex.”

Ruby said aside from needing a land line and committing to 20 to 40 hours a week, a PSO has to be outgoing, imaginative, knowledgeable about sexual fetishes and, most importantly, able to offer a human connection over the phone.

“You need compassion. Sometimes the call is the only nice part of their day,” Ruby said. “They may have really crappy lives. I like to think I’m giving them a little bit of sunshine.”