In this user guide it assumes that all phones have Line keys 2 though 5 Programmed as Hold 1, Hold 2, Hold 3 and Hold 4.
While on a call you can press any of the Hold Keys that are green. The call will be placed on hold/park and the associated Line Key will turn red to indicate that the call is now on hold at the said location.
Any user can press the red Park/Hold key and be connected with the call.
The Line keys 6 through 100 will vary from install to install. These are programmed per install and per individual user needs.