title: How to "multiplex" multiple sms conversations from one or a few server phone numbers
body: <p>So here's the use case: we want to bridge chats from our mobile application to sms, so that they don't have to use a custom messenger app.  Server-side, using a service like Twilio, would you have to provision separate phone numbers for every session/conversation?  If so, that would be prohibitively expensive.</p>
  
  <p>In a simple use case, one server phone number can handle all the incoming sms messages from multiple clients and conversations.  It can, based on the client sender's phone number, discriminate what conversation the sms belongs to and send appropriate replies back filtered to the phone numbers of the participants in each conversation.  This would allow multiple conversations to be managed by a single server phone number.</p>
  
  <p>However, in an enhanced use case, if the client is in more than one conversation at the same time, there is no easy way to determine which conversation the client's reply was for from the server unless we can somehow embed info in the reply text itself.</p>
  
  <p>Is that just a limitation or is there a way to allow for this enhanced use case?</p>
  
  <p>Is there something in Twilio or in SMS technology, or in the way that I'm thinking about this that would allow that conversation info to be sent back in a fool-proof way (not making the user manually type the conversation id for instance) to allow multiplexing multiple concurrent sms conversations from the same client user?</p>