AT&T MERLIN LEGEND Release 4.0 Feature Reference page 54

Feature Reference
System
Access/Intercom
Buttons
Transfer
54
Auto Dial
When you press an inside Auto Dial button, the system automatically
selects an SA or ICOM button and turns on the speakerphone. When
you press an outside Auto Dial button, the system automatically selects
an outside line button in Key mode, a prime line button in Behind Switch
mode, or an SA button in Hybrid/PBX mode.
You can press inside Auto Dial buttons instead of dialing extension
numbers to transfer calls. To use the One-Touch Transfer option, you
must program inside Auto Dial buttons for extensions to which you
transfer calls. When an operator transfers a call and it returns
unanswered, the green LED next to the Auto Dial button flashes to
indicate the extension from which the call is returning. Only system
operators receive this indication.