I actually worry about startup's that don't generate revenue, especially tools that people can grow dependent on. I know a few teachers but, I'm weary of sharing this with them if you disappear in 6 months due to lack of funding.
Text message's, although cheap, are not free.
What are your plans for revenue and why not charge $2.99/month?
It's because they are charging $9.99 instead. If you look at the FAQ you will see the pricing breakdown. It's only free to use for a limited number of texts. There should be some text on the page that says something like, "free to use for small classrooms and affordable plans for large ones."
Text message's, although cheap, are not free.
What are your plans for revenue and why not charge $2.99/month?