Companies are using Twitter to help out their business in four ways:

1. Directly- Business people are using twitter as a marking or public relations channel
2. Internally- Business people are using twitter to share ideas or communicate about what projects they are working on
3. Inbound Signaling- Using twitter to see what is being said about their companies as well as others

http://www.readwriteweb.com/enterprise/2009/03/4-ways-companies-use-twitter-for-business.php