It is a well known fact that Twitter does not have a revenue model yet.
The company has been working on ensuring the quality of service while they work out on a revenue model.
Twitter is likely to announce something soon enough as it is almost time they show some results to the investors.
The micro-blogging industry giant has hinted that one of the possible ways to generate revenues from the service is through charging for business accounts.
This means that any company which wants to do business through Twitter could soon have to pay for using the service.
It would be however tough for Twitter to justify the costing if they do not offer something more to the paying customers.
Once you are providing a certain service for free, it becomes very hard to charge for it at a later stage.
Maybe, Twitter is working on providing certain additional features to the business customers which would make it worth the money charged for it.