Bosses at Twitter think they’ve solved the site’s major problem: how to make cash without alienating the user base.

The company has confirmed it will offer premium accounts where businesses pay a subscription fee to access extra services, but maintains that the existing system of free accounts for all will remain unchanged.

Co-founder Biz Stone told Reuters he believed firms would pay to access services which will help them get “even more” value out of Twitter.

The firm isn’t saying anything else about what services a premium account would include. One possibility is that it would include getting priority access to Twitter’s servers, making such users less likely to see the dreaded “fail whale” that appears when the site is overloaded. That would be stretching the promise to maintain services to free account users: the functionality would remain unchanged, but the reliability would potentially deteriorate.

It’s also possible Twitter could be thinking of offering features such as an enhanced search or monitoring service. But it’s tough to see how the site would make those marketable without restricting the access that existing third-party services such as TweetDeck and Twirhl currently enjoy.

The news comes as Twitter announces it’s first significant revenue stream, a sponsorship deal with Microsoft. In return for its payment, the Microsoft branding will appear on ExecTweets, a site which carries a stream of Twitter posts from leading business executives.

Twitter has denied its received any cash from people who appear on ‘Suggested Users’, a list which appears alongside the site’s tools for finding existing friends on the service. As appearing on the list greatly increases the number of people following your messages, it would be a valuable opportunity for anyone using Twitter as a promotional tool.

However, Stone says spots on the list are not for sale. Instead the firm uses an automated program for identifying users with lots of followers who post regularly. Staff then check these results and pick out those which they believe people will genuinely be most interested in.