While others have rightly pointed out pollanywhere, I'm looking to go beyond just polls. I have text based discussions and will be adding audience annotations (useful for small meetings, brainstorming, etc) in the near future.

Not really related, but I had another idea (more of an art project) about installing a projector in a public place or maybe on a uni campus that you could text to and have it project your message. Some kind of experiment of uncensored amplification of speech.

They do this at a lot of conferences, at least using Twitter instead of SMS.

Check out https://www.polleverywhere.com/

Haha, cool. I think I could compete with that, as a hobbyist business for non-profits in my home market at least.