Twitter boss Biz Stone has unveiled more about the micro-blogging service's plans to make money revealing that paid-for commercial accounts will roll-out this year, in an interview with the BBC.

Stone insists Twitter will stay free for individuals, and for businesses too, stating "Twitter will always be free to everyone whether it's commercial or personal", but that paid-for commercial accounts will offer a "special layer of access" that will include analytics and feedback.

There's also the possibility of revenue from licensing and syndication possibilities, said Stone, such as the deals recently done with Google and Bing in order to see Twitter content show up in search results.

The interview comes as Twitter has changed its "what are you doing?" tagline above the box where users enter their tweets to "what's happening?"

In a blog post, Twitter explains the change is to reflect the changing way in which the service is used, with more companies tweeting rather than just individuals:

"People, organizations, and businesses quickly began leveraging the open nature of the network to share anything they wanted, completely ignoring the original question, seemingly on a quest to both ask and answer a different, more immediate question, 'What's happening?'"