Voice/Data Terminal Bottom View | AT&T 8520T instruction

Mute button	For turning off (and then back on again) the microphone
	of the handset or the speakerphone so the other person
	on the call cannot hear you.
Redial button	For automatically redialing the last number you dialed
	from the dial pad.
Softkeys	The 10 unlabeled buttons located on both sides of the
	display (5 buttons on each side) correspond to words on
	the display screen. Softkeys are used along with display
	control keys to access or create a personal Directory of
	frequently-called numbers, a Call Log of the most recent
	incoming and outgoing calls, and such features as
	selecting a personalized ringing pattern, doing a self-test
	of your voice/data terminal, and setting the
	speakerphone and the clock.
Speaker button	For turning on and off the speakerphone or the
	listen-only speaker.
Telephone number card	For noting the area code and telephone number of your
	voice/data terminal.
Transfer button	For transferring a call to another voice/data terminal.
Volume control button	When on a call, used to increase or decrease the receive
	volume of the handset or speakerphone (according to
	which one you are using). When you are not on a call,
	the Volume control button is used to increase or
	decrease the volume of the ringer and the tones.

Routing Line RS232

channel jack connector

Adjunct	Handset	Handset cord
jack	jack	routing channel

AT&T 8520T manual Voice/Data Terminal Bottom View