The Avaya 6402 is a single-line telephone with six fixed feature buttons: a listen-only Speaker button, a feature button that allows you to use the dial pad keys for up to 12 features assigned by the system manager, a red Hold button, a redial button, a transfer button that can also be used for the test feature, a conference button that can also be used to select a personalized ringing pattern, a red message light, and a volume control button. This phone has no display.

The Avaya 6402D is a single-line telephone with six fixed feature buttons: a listen-only Speaker button, a Feature button that allows you to use the dial pad keys for up to 12 features assigned by the system manager, a red hold button, a redial button, a transfer button that can also be used for the test feature, a conference button that can also be used to select a personalized ringing pattern, a red Message light, and a Volume control button. The 6402D also has a two-line by 16-character LCD display.

The Avaya 6408D+ is a multi-appearance digital telephone with eight call appearance/feature buttons. The 6408D+ has a two-way speakerphone and a two-line by 24-character display. The 6408D+ also has six standard fixed feature buttons: a speaker button, which can access the two-way speakerphone, mute button to mute the handset or speakerphone microphone, a red hold button, redial button, transfer/test button for transferring a call or testing the lights and display on the telephone, and a conf/ring button for setting up a conference call and for selecting a personalized ringing pattern.

The Avaya 6416D+M telephone is a multi-appearance digital telephone with 16 call appearance/feature buttons. The 6416D+M has a two-way speakerphone and a two-line by 24-character display. This telephone also has six standard fixed feature buttons: a speaker button, which can access a two-way speakerphone, mute button to mute the handset or speakerphone microphone, a red hold button, redial button, transfer/test button for transferring a call or testing the lights and display on the telephone, and a Conf/Ring button for setting up a conference call and for selecting a personalized ringing pattern.

The XM24 Expansion Module is an optional device, which can be connected to a 6416D+, 6416D+M, 6424D+, 6424D+M phone, or to a Callmaster® V Digital Voice Terminal to extend the number of call appearance and feature buttons available. The XM24 adds up to 24 additional call appearance and feature buttons.