I made a similar thing a few weeks ago (though much more crude) to use amongst a group of friends who were living in the same apartment complex. One thing I realized after I made it is that this general system of texting with Twilio is not going to be cheap since if you have a lot of users each text could cost a good portion of a dollar, nevermind if there were a conversation. You going to foot the bill or have you found a way to make it cheaper?