Phones are equipped with a number of different buttons or keys. Phones have number keys (0-9) for dialling, as well as so-called function keys. The number and type of function keys depends very much on the phone and whether or not it is connected to a PBX. The simplest function keys that are present on almost all phones are the redial key, "#" and "*". With these keys alone users can control many of the features modern telephone networks offer.
In companies with large and very powerful PBXs so-called system phones are often used. These support functions and features of the telephone system in question and, depending on the type and use, have different kinds of function keys. Frequently used function keys include:
- Speed dial keys, for calling predefined numbers with one touch
- The redial button, to redial the last number called
- The recall key, to put your call on hold so you can dial another number
- The call forwarding key, to divert all incoming calls to a predefined number or the answering machine
- The conference call button, for setting up multiple simultaneous conversations and initiating a conference call.
- The Busy Lamp Field key (BLF), to display which colleagues are currently in calls.
- The intercom key. By pressing the function key the user is directly connected with the loudspeaker of the answering party.