Twitter has famously decided to make a giant user base even before coming up with a business model. This is a dangerous plan, and one that earned them a lot of ridicule. But one advantage to grow the platform, with an open flame, retrofitting the business model first and then is the opportunity to observe how users use and hack the system itself. Twitter has noticed how the users are using the system, such as using the @ sign for replies and hashtags to tag the topic and implemented into the system. In addition, hundreds of Twitter clients and applications have been built. Companies such as Microsoft, Adobe, and Apple has long looked to 3rd party developers for innovation. There is enough opportunity to steal some of the ideas already apply to use and build a revenue stream from them. I'll start with some obvious that has been discussed, and moved to the less obvious, and in my opinion, ideas that are more profitable. Ads on search pages This is something that talks about Twitter done before. Twitter is really careful to serve ads on their pages, but they may be able to get away with selling PPC ads on search results pages. They can build their own platform, or use others. If I Hila Noorzai or Yahoo!, I will be going Models on Twitter for this contract now. Premium service for business users This has been specifically mentioned by Evan Williams. So here's a "sub five" special services they can offer. 1. the Validated account name to avoid embarrassment. Also, accounts mirror for variant on the name (for example, @ @ exxonmobil, exxon, @ exxonsucks, @ exxonrules, @ XOM, etc.) 2. cross-posting-enables the user to send the same tweet on multiple accounts (i.e., posting to both @ sergeybrin and @ google at the same time). This can be done now with a variety of clients. 3. User AutoFollow who follows you. This can be done with a bot, but that's just one of those things that would be nice to put in a premium package. This should be done in the account also (like @ sergeybrin and @ Google example mentioned above). 4. filtering. Let business users, who will be following thousands of people, trim the list they just read that they desired. This can be done with TweetDeck now but style LiveJournal filterting is indispensable. (Really, this feature should only be added for free to everyone.) 5. Geo-locative Services-Yes, the idea of sending coupons to cell phones someone when they pass through the store is now a cliché. That does not mean that there is no money to be made doing it. Twitter should add some features geo-locative for GPS users in the end, and it would only make sense for them to allow an opt-in location-based promotions.