AT&T MERLIN LEGEND Installation & Maintenance Manual page 34

System Description
Key Mode
In the Key mode, each outside line appears on a button on one
or more multiline telephones. The line buttons allow users to see
activity on other telephones, join conversations, place calls, or
receive calls. Separate intercom buttons are used to make and
receive internal calls.
A Key system automatically assigns the first eight outside lines to
all telephones. This arrangement can be customized through
system programming by assigning lines to individual telephones
or to selected groups of telephones.
Behind Switch Mode
In the Behind Switch mode, the system is connected to a
Hybrid/PBX or Centrex system. This other system (called the
host) provides the interface to outside lines and some features.
A Behind Switch system assigns only one line (called a prime
line) to each telephone. Outside lines to telephones or groups of
telephones are assigned through system programming. In the
Behind Switch mode, people can use the special features of
both the MERLIN LEGEND Communications System and the host
system.
Modes of Operation 1-3