title: how to associate received sms messages (via twilio) to specific user in my rails app
body: <p>I'm making an app that sends text messages to a group of people and then people can respond to the text. I want to be able to record the response, know who sent it, and associate it with the user who sent the original message. I've gotten the sending working, and I've begun putting together receiving sms messages but i'm confused. If twilio sends a post request to my server with the from number and message, how will I know which of my users sent the original message? </p>
  
  <p>what if two different users send a message to the same person around the same time? what's the best way to handle this? do I need a separate 'to' number for each of my users? seems like that would get quite expensive. also, if each user has multiple campaigns (messages), how would I associate a response to a specific campaign?</p>
  
  <p>i'm building a rails app.thanks</p>