A:Answer Andi - When the VTech CM18445 or any of its extension is in use on one line and another call comes in on the opposite line, the current unit that is in use will not ring. You will only hear a beep to alert you that there is a call on a different line. However, if there are other extensions connected to the main console and those extensions are not in use, you will hear an audible ring. If you have other inquiries, please contact VTech Customer Support for further assistance at 1-800-595-9511. We are open from 9:00 AM to 3:00 PM, Mondays through Fridays. When calling, please have your model number handy: CM18445. Thank you! - VTech Support