Twitter does not yet have a revenue model. Here’s one to ponder:
The service should continue to be free for subscribers. To generate revenue I think Twitter should sell small ads on the direct messaging page and those ads should be targeted based on hash tags and other behavioral targeting information gathered. If, for instance, someone uses the hash tag #iranlelection, maybe their direct messages will contain a small ad for The New York Times. In addition, I’m wondering if the keyword bidding and pay per click method pioneered by Google Adwords would also be smart.
Think about it and get back to me. Peace!