NEW YORK (AdAge.com) -- In India, thousands of consumers are going from tweeting to bubbling.

A hot new social-networking service dubbed Bubbly, which is essentially a voice-based Twitter, is quickly gaining popularity among Indians. And thanks to Bollywood celebs being early adopters, Bubbly is growing virally and with virtually zero marketing spend.

Bubbly is the brainchild of 5-year-old mobile and social app firm Bubble Motion, which is based in Silicon Valley and Singapore. Its first product was BubbleTalk, a person-to-person voice-messaging service that, instead of SMS, sends mobile audio messages and has about 100 million users now.

According to Bubble Motion's CEO Tom Clayton, after devoting time to BubbleTalk and other mobile voice-messaging services, "along came the social-media boom and we started to play with a lot of social-media applications." That led to the idea of audio messages going not just to one person, but to a much larger audience of followers.

In rolling out Bubbly, Mr. Clayton plans to skip North America and Europe and focus on fast-growing, mobile-savvy markets such as India, Japan and Brazil.

Here's how Bubbly works: Anyone can sign up to follow a friend, family member or favorite celebrity or brand. Posting messages and following is free, and once a new message has been recorded and sent out, users get an alert. If they choose to listen, they pay for the airtime.

Most messages are less than 30 seconds long, and there is currently a cap of one minute.

To post on Bubbly, a user dials a short code, like *7, records a message and hangs up. To listen, tap in another code, like *2. It works on any handheld device, and messages can be posted to Bubbly while still withholding phone numbers for privacy.

Bubbly hasn't launched officially, but the service saw an estimated 500,000 users in about four weeks after some of Bollywood's biggest stars started using it, including Aamir Khan and Kareena Kapoor, who were talking about it ahead of the premiere of their hit film "Three Idiots" (which recently swept India's Filmfare Awards). "It's personal and it's easier for a celeb" to connect with their fans using Bubbly rather than a web-based service in which an agent or PR firm might be writing messages, said Mr. Clayton.

Media networks in India are showing signs of interest too; the first major media brand to sign on there is the BBC, which is experimenting with the service as a way of disseminating breaking news (listen to audio clip below, in Hindi). And other networks are in talks to potentially follow suit.

Bubbly's business model is based on its revenue-sharing partnerships with telecoms. In India, that includes two giants, Reliance Communications and Bharti Airtel.

In a country where many have access to cellphones but far fewer to the web, this type of mobile blogging service seems to make sense. By some estimates, India has the fastest-growing population of mobile phone users in the world as cellphone operators add millions of new customers each month. By 2012, India may have 650 million cellphone users.

To use Bubbly for brand engagement and promotion, a celebrity spokesperson could record messages about brands or send a "bubble" from the set of a forthcoming movie to build buzz. Brands themselves can also bubble short radio-like ads over cellphones, although it's up to users to opt in.

Bubbly has been beta-tested in places such as Egypt, where BMW bubbled a promotion to visitors to a retail location, and Citigroup used it to send out ads and Vodafone to deliver the latest ringtone.

But Mr. Clayton said Bubbly is targeting five major global markets -- India, Japan, the Philippines, Indonesia and Brazil -- because they all offer large, mobile-savvy populations whose telecoms and cellphone users are "also open to cool, new innovative stuff." A web component may have a role in the launch of Bubbly in Japan, but in most markets the focus will remain on a mobile-only version of Bubbly for now.

And while the mobile operators Bubbly partners with might tout the service in their own ad campaigns, traditional advertising isn't on Bubble Motion's agenda anytime soon. Part of the company's goal, and the mission of its VP-marketing and product management, David Still, is to "grow to hundreds of millions of users through viral and word-of-mouth marketing with very little, if any, marketing spend," said Mr. Clayton. "In each country we have a different strategy, but a lot of it is around entertainment and sports [celebrities]."