 <p>As in the Hayes modem control commands? These are the commands used to gain the *AT*tention of a modem and cause it to interact with the phone system and/or computer (to test, read, set and execute commands). A tutorial can be found here: <a href="http://www.engineersgarage.com/tutorials/at-commands" rel="nofollow">http://www.engineersgarage.com/tutorials/at-commands</a></p>