Is there a way to turn off the following tone:

When i'm calling on my Cisco ATA-112, i hear a tone when someone else is ringing me on that line. I get the tone every couple of seconds during my call, till the moment that the person that calls hangs the phone. Is it possible that the second caller gets a busy tone or something else? But I really want to disable the annoying tone that disturbs my conversations.

Hope someone can help me!