User`s guide

On steady (with telephone on hook and idle) = background music is
turned on.
Flashing = feature programming is in progress.
Above the MUTE button:
On steady = called party cannot hear your conversation.
Above the SHIFT button:
On steady = shift mode is activated to allow access to second level
speed dial numbers programmed at DSS button locations.
GCA70–249 Introducing The Telephone
Non-LCD Reference Manual 1 – 11