Its easy. Just to teach you a few trick Commissions on user purchases — Setup a service that allows users to buy products through this. User would need to setup an account with you with their credit card (or PayPal info, or a deposit into this proposed payment service) stored. I imagine a user could be browsing Wired magazine and be able to quickly purchase a subscription for $10 by ripping out their cell phone, Twittering a code like “d buy wiredâ€, with a confirmation coming back to the user and them approving the confirmation possibly using a password, then the transaction occurring. Charge for access to your Twitter messages — Your username can be private and only your friends can receive/view your twitters. Thus, if you had valuable/timely information — you could have a subscription-based service where you charge $X for people to be your friend, and then they would have access to your twitters. Thus, a celebrity could charge for this — or a newspaper might do this to give you access to the news first — or some blogger that finds online shopping deals could send them to you … basically, if the user wanted to be “in the know†for whatever offering, they’d pay $X for access (per week or month). Note: You’d have to verify their subscriptions — and if they haven’t paid for the month, you’d remove them as a friend from your Twitter account.