Your stats are unfortunately pretty small when it comes to advertising dollars. The fact is that Twitter doesn't lend itself to monetizing on the messages itse

Your stats are unfortunately pretty small when it comes to advertising dollars. The fact is that Twitter doesn't lend itself to monetizing on the messages itself, and as that is how your bot operates that makes it quite difficult. Twitter spam is pretty unwelcome in general, the "friending" (when users follow each other) is treated as a pact not to create noise. I think given time it will become more acceptable as Twitter ages and more services spring up that people want to use and need funding to survive. I don't think Freemium will work for you, this isn't a necessary service and that's what is required for user conversion from Free to Premium. The webpage login may work, but now you're just giving the user a specific action which means any ads you show them have a very low chance of catching their eye. I think my suggestion is check out Magpie or something similar, and make one "broadcast" tweet rather than a DM to each user. They have to be following you to get your DMs so they have to get your tweets. That's my suggestion.