I think most of the "trying Twilio out" apps published barely scratch the surface of the potential, even though many are cool. (I did one, too: time-aware phone secretary, which has totally resolved my "My family does not understand that 3:30 AM Japan time is a bad time to call for a chat" problem.)

Because everything is on your web server, you can seamlessly move data between the phone and an arbitrarily complex web interface. I think that basic pattern allows multiple disruptive applications for any industry you care to name.