Siemens HIPATH 8000 - Manual (Page 13)

General information
13
Single-line telephone/multi-line telephone
Your OpenStage 40 is a "multi-line telephone". This means that multiple
lines can be configured, which is not the case with single-line phones.
Each line is assigned an individual phone number which you can use to
make and receive calls.
The programmable sensor keys function as line keys on multi-line phones
page 23.
The "Overview" tab on the telephony interface provides information about
the lines configured on your phone and the current status of each line
page 31.
A number of specific features must be considered when using a multi-line
phone to make and receive calls
page 95.