AT&T 993 - Manual (Page 19)

6
Getting started
Optional headset
Make sure the headset is firmly plugged into the headset jack under the
rubber flap on the right side of the telephone. There is a low pitch (error)
tone if you press
HEADSET when the headset is not plugged in.
For hands-free telephone conversations, use any industry standard 2.5 mm
headset (purchased separately). For best results, use an AT&T 2.5 mm headset.
To order an AT&T 2.5 mm headset, visit our website at
www.telephones.att.com
or call
1 (800) 222-3111.
In Canada, dial
1 (866) 288-4268.
NOTE: If the sound quality of the headset is poor, try unplugging it, and firmly plugging it in
again.
Plug 2.5 mm headset into
the jack on the right side
of the telephone base
(beneath the small rubber
flap).