AT&T MERLIN LEGEND Release 4.0 Feature Reference page 537

Feature Reference
caller's voice over the speakerphone. Because voice-announced calls
cannot be made to single-line telephones, a call made on this button to a
single-line telephone is a ringing call even if the single-line telephone has
a speakerphone.
Originate Only. This button is used only to make inside calls. Calls are
not received on this button. Its purpose is to ensure that the user always
has a button available to make or transfer calls, establish conference
calls, answer call-waiting calls, or pick up parked calls. The button can
be programmed for either Ring or Voice operation.
The default attribute for all ICOM buttons after the factory settings by telephone
type is Ring.
In Key mode, the factory setting for Automatic Line Selection (ALS) for multiline
telephones is a sequence of outside line buttons. The factory setting for ALS on
single-line telephones is an ICOM button.
In Behind Switch mode, the factory setting for ALS for both multiline and
single-line telephones is the prime line.
Ringing for all types of ICOM buttons is set by default to Immediate Ring and
can be changed to Delay Ring or No Ring (see "Ringing Options").
NOTE:
ICOM buttons are not shared.
Considerations and Constraints
At least one SA or ICOM button must be assigned to each extension in the
system.
SA or ICOM buttons can be assigned or removed only through centralized
telephone programming.
On a multiline telephone, SA or ICOM buttons can be assigned only on buttons
1 through 10.
Any SA button can be the principal extension for up to 16 Shared SA buttons
on other telephones. Any multiline telephone can have up to 28 SA or
Shared SA buttons, at least one of which must be an SA button. No SA buttons
may be assigned beyond line button 10, although Shared SA buttons may.
The maximum number of system users that can be on a call on a Shared SA
button (including the principal extension) is three.
When a call is received at the principal extension, it rings on the principal
extension's SA button as well as on all corresponding Shared SA buttons.
System Access/Intercom Buttons
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