YAC is a Caller ID system that uses the modem in your computer to monitor incoming phone calls. When a phone call is received, YAC displays the Caller ID info on the computer screen. This utility can also notify programs called YAC Listeners on the network. These listeners receive and display Caller ID information at the same time as the computer attached to the phone line. YAC can be used to send text messages to the listeners on your network as well.