title: What software/hardware is needed to receive (and respond to) SMS from multiple machines?
body: <p>What software/hardware do the SMS centers use to make the following possible:
  An SMS is received to a number. The SMS is routed to one of X machines (Mac/PC). An operator responds to the sender.</p>
  
  <p>It seems that a GSM modem is needed?  However, I have trouble understanding the architecture.</p>
  
  <p>Is there any plug-and-play solution? Are there any specific frameworks/languages/tools for building such a system? How do you route incoming messages to machines? How do you queue outgoing text messages? </p>