1. put an ad after every 140 character profile update. ie, drink a cup of tea.
2. Send out an advertisement every 10th -50th twitter. Thus you may receive 10 news announcement.
3. Pay-per twitter massage- Suppose your name is 'ana_jobs' . somebody in twitter finding your name on twitter with jobs, suppose you have 2000 followers on twitter if he wants to be your friend then all your followers may post article of 140 charecter. then you can charge your friends or employees for posting massage.
4. Charge for accessing your twitter massage. but you would verify your new request subscription and if they dont pay you after a month then you simply remove them from twitter friend list.
5. Commisions for user purchases--- Set up a user to buy your products through this.