Ari Graynor isn't your best friend, but she plays one on screen. A lot.

Since breaking out as the perma-drunk Caroline in "Nick and Norah's Infinite Playlist," Graynor has played a variety of supporting confidants in "What's Your Number," "Celeste and Jesse Forever," "Whip It" and the upcoming "10 Years." However, it's the BFF she plays in "For A Good Time Call..." that could launch Graynor into the same class of leading comedic actresses as Anna Faris and Drew Barrymore.

Co-written by Lauren Anne Miller and Katie Anne Naylon, and based on their relationship and Naylon's time spent as a phone sex operator, "For A Good Time Call..." is that rare Hollywood film: A romantic comedy about female friendship. Graynor stars as the screen incarnation of Katie in the film, a role that was written for her after Miller and Naylon became friendly with the actress. (Miller, meanwhile, co-stars, playing a slight variation on herself.)

Graynor -- who started a very active Twitter account during the press rounds for "For A Good Time Call..." -- spoke to HuffPost Entertainment about why the movie is the most important project of her career so far and why it's important to choose unrealistic looking dildos when making a sex comedy.

You've been a supporting actor in so many films -- what was the hardest part of transitioning to a leading role?
There was very little that was difficult about it -- or any more difficult than being a supporting player. The work is essentially the same. It was such a welcome challenge, however -- especially executive producing the film as well. There was a different stake in this film for me, and certainly for our entire team: Katie and Lauren wrote it, Lauren acting in it, Katie and Lauren producing it, [director] Jamie Travis' first feature -- this became our baby. The four of us worked so closely together before production that a lot of it became a different sense of responsibility for creating what we knew we wanted to create, and just trying to do everything we could do to that in the best way -- as an actor, producer, helping with the story, the script, just all those pieces. Just saying, "OK, if we're going to take this chance on ourselves, we better make this the best thing we can make."

This is a role that was expressly written for you. What did you think when you first read the script?
I loved it from the second I started reading the script. It was so fresh and it was so mind-boggling to me that there are not more movies about female friendship. Being women, your friends are such an enormous part of your life, and it's been such a void for movies -- especially in the last 10 or 15 years. This movie has a bit of a nostalgic feel back to some of the '80s movies we all loved with Shelley Long, Goldie Hawn, Bette Midler, Diane Keaton and Lily Tomlin; that culture of movies with really strong yet vulnerable women involved in stories that were not fully about getting the guy. I thought that Lauren and Katie did such an incredibly smart thing by subverting the romantic comedy and using it as a friendship love story instead. Then the setting of the phone sex was such a clever, naughty, delicious piece.

Was there anything you had to say that just went so over the top that you couldn't believe it?
No, I mean, the script I read originally was much broader than our shooting script. There was a man that worked at a porn shop who drove a dick car. We ended the movie on the "TODAY" show having written a book about phone sex. There were a lot of different incarnations of the script. When the four of us became the cohesive unit that we became, so much of our journey was about working through it to make the script and story and friendship feel as real as possible. Then, with that, it allowed the phone sex piece to take on a fantastical, fun element. We always wanted it to be funny, rather than overtly sexual or titillating. I don't know -- I guess it takes a lot ot make me blush over that kind of language. The irony is, we wouldn't bat an eye at all the crazy and outlandish stuff, it was more of the intimate moments. The phone sex call between me and Sean (co-star Mark Webber) and some of the scenes with him, where the intimacy was more real and we got a little bit blushy. We had to pull back on it in the editing and shooting of it.

You mention some of the broader aspects of the film: I'm reminded of the scene where you and Lauren are inspecting a bunch of dildos and your character puts one in her mouth. So, a) are you ready to have that scene appear as one of your top choices in Google image search, and b) how much discussion went into how big the dildo should be?
That's so funny. I had not really thought about the Google image search of the blue dildo in my mouth until this moment. So, thanks for bringing that up. I'm totally terrified. No, but I purposefully did chose the least natural looking dildo for that moment so were that to happen, it wouldn't look overtly sexual. It was a very funny set with those props. You just become immune so quickly: "You want the dildos in or out of this one?" "We'll have the dildos in!" We had a dildo washing station that day. We would say, "We need dildos that are bigger. Do we have anything that's bigger?" Then they get it. In the world of comedy it's just about catching the eye off-guard and being silly and not taking yourself too seriously.

Switching gears: When you were making "Nick and Nora's Infinite Playlist" did you realize how important that film was going to be to your career?
I definitely knew that was an incredibly special project and an incredibly special character. The way I felt about that is the way I felt about this too: Those kind of characters in those kind of movies don't come along every day. There's so many great movies and great stories to be told, but it's really hard to write a surprising, full-bodied, super-alive female character. Especially in comedies. I wanted to play Caroline so, so, so, so, so badly, and I feel so lucky that I got to be a part of that. And I felt very similarly when I read this script.

The challenge is that we made an independent film and no one really knows me and Lauren. It's a movie starring two people that people don't know, and I think some people hear phone sex and get nervous. But I know people love the movie once they see it, and I think that if we can get people in the seats and have them go in with an open mind, they'll be pleasantly surprised and this could find a special place in their hearts.

To that end, I noticed you joined Twitter recently. How are you enjoying it so far?
Twitter's a lot of work! That's the first thing I would say. There's so much pressure to be funny. The reason why I joined was certainly to get the word out about this movie and one of the best parts of it has been communicating -- I feel silly using the word fans; that feels like a pretentious term coming out of my mouth -- but it's so nice to communicate with people who have any kind of enthusiasm or excitement for the movie or me or anything like that. But it is hard! It is a lot of work. There's pressure to come up with something genius every time. I feel like I keep letting myself down with my Twitter posts. I have to start keeping a journal of rough drafts of prophetic ideas about the world.

You're on record as being a huge Barbra Streisand fan and you're in "The Guilt Trip" with her later this year. Did you get to share any scenes?
I'm not going to say anything about that movie -- but I'm so excited to be a part of it. That is for sure. Otherwise, mum's the word.

Loading Slideshow...
  • Writer Katie Anne Naylon, writer and actress Lauren Miller, actress Ari Graynor and director Jamie Travis attend Day 2 of the Variety Studio during the 2012 Sundance Film Festival on January 22, 2012 in Park City, Utah. (Photo by Alexandra Wyman/Getty Images)

  • Katie Anne Naylon and Lauren Miller attend day 2 of the Variety Studio during the 2012 Sundance Film Festival on January 22, 2012 in Park City, Utah. (Photo by Alexandra Wyman/Getty Images)

  • Katie Anne Naylon attends the 'For A Good Time, Call...' premiere during the 2012 Sundance Film Festival held at Eccles Center Theatre on January 22, 2012 in Park City, Utah. (Photo by Jemal Countess/Getty Images)

  • Actress Sugar Lyn Beard, writer Katie Anne Naylon, writer and actress Lauren Miller, director Jamie Travis, and actresses Ari Graynor and Nia Vardalos pose for a portrait during the 2012 Sundance Film Festival at the Getty Images Portrait Studio at T-Mobile Village at the Lift on January 22, 2012 in Park City, Utah. (Photo by Larry Busacca/Getty Images)

  • Lauren Miller stars as Lauren and Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Ryder Sloane / Focus Features)

  • Lauren Miller stars as Lauren and Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie and Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie and Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Justin Long stars as Jesse in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Ari Graynor stars as Katie, Justin Long stars as Jesse and Lauren Miller stars as Lauren in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Nia Vardalos stars as Rachel Rodman in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Don McManus stars as Scott and Mimi Rogers stars as Adele in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • Mark Webber stars as Sean and Ari Graynor stars as Katie in Jamie Travis' 'For A Good Time, Call...,' a Focus Features release. (Focus Features)

  • This is the trailer 'For A Good Time, Call...' starring Mimi Rogers, Seth Rogen and Nia Vardalos. Former college frenemies Lauren and Katie move into a fabulous Gramercy Park apartment, and in order to make ends meet, the unlikely pair start a phone sex line together in this comedy.

Also on HuffPost: