While not providing any details, Stone told the Wall Street Journal that fee-based services are under development. As to those businesses piggybacking on Twitter's free service, Stone said he doesn't consider them competition.
"We want to work with those companies that are already making an effort," he told the newspaper.
Twitter recently hired a product manager to head development of commercial accounts, which would offer additional features for a fee, Stone said.
Twitter allows users to send messages of no more than 140 characters to people who subscribe to them. The messages, or "tweets," can be embedded on Web sites and blogs and received via PC and mobile phone. The topics range from the mundane activities of everyday life to eyewitness accounts of a plane crash and interviews with politicians.
Twitter has attracted millions of users, and its popularity has attracted businesses, which use the service to market products. Some have started brokering ads that run alongside tweets.
Stone has said before that the San Francisco startup was looking at ways to draw revenue from the service. In mid-February, following an interview with the British trade publication Marketing, Stone put out a statement clarifying his remarks, which sparked speculation on premium accounts.
"Twitter will remain free to use by everyone -- individuals, companies, celebrities, etc.," Stone said on the company blog. "What we’re thinking about is adding value in places where we are already seeing traction, not imposing fees on existing services."
A recent round of venture funding valued the company at $255 million, according to the Journal. Nevertheless, Twitter executives have yet to make any money on the service.
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