The expansion keys can be assigned the numbers of frequently called participants and be individually labelled. Thus, it is possible for the user to initiate a large number of calls directly with a single push of a key. Keypad expansions often have 40 or more programmable keys. Some allow cascading of several expansions and thus provide almost 100 or more programmable function keys.
Telephone users whose job is to receive calls and transfer or put calls through to other participants, find an extremely useful tool in the form of a specially designed keypad expansion. Information on the status of a call or a line is provided by LED indicators. Thus, e.g., incoming calls, calls on hold or parked calls can be identified at a glance. Specific keypad expansions, in interaction with the telephone system, enable the user to determine how many calls are in progress at the moment, which participants are free or for how long will calls be in queue.