Created by Gervais with voice technology company CloudTalk, the free app is a social media service that involves users speaking to each other.
Working similarly to photo-sharing service Instagram, Just Sayin' allows users to share voice- and video-based messages with their friends and followers on Facebook and Twitter. They can also share photos and text.
Available to download now on iPhone, iPod Touch and iPad, an Android version will follow by the end of the year.
Gervais, credited as Just Sayin' partner and creative director, said that the app is to radio what "Twitter is to newsprint".
In a statement issued to The Hollywood Reporter, the Office creator added: "Making the human voice a natural part of any social web experience is the next big thing.
Features on Just Sayin' include the choice of one-to-one or one-to-many voice conversations, real-time notifications, and cross-posting on both Facebook and Twitter.
In addition to Gervais, the app's celebrity users include rock stars Nikki Sixx, Tommy Lee and the band Crossfade, along with female football star Brandi Chastain and 2008 US Presidential candidate Mick Huckabee.
Gervais teamed up with Just Sayin' founder David Hayden around a year ago and helped develop the app and test it in public beta.
"I've had a hand in seeing the development of this new idea of public conversations, and importantly, experimenting with what kinds of conversations work and which don't," he told Entertainment Weekly.
"I've always been fascinated with what fascinates people. I'm quite good at taking in the common consciousness and reflecting it back, I think… This is just another forum. Another playground. Creativity is all about playing."
But in testing, Gervais arrived at a rather surprising realisation: "I hate my voice. In my head, I sound so much more erudite and articulate."