Four-line accessory handset is designed for use with AT&T Four-Line Corded / Cordless Small Business System with Extendable Range & displays four lines. Design includes push-to-talk speakerphone & 50-name / number Caller ID history, 100-name / number phonebook directory, volume control, ringer volume control, low-battery indicator, intercom, mute, redial, hold function & 10-name redial.