Many models of supported telephones are capable of advanced functions using Busy Lamp Fields (BLF), Speed dials, function toggles (such as queues, follow me, etc.).
Depending on client requirements, a list can be configured which can be applied to one or more phones which will allow any linked phone to monitor the current status (presence) of other phones on the system.
The important thing to keep in mind, is that while the order of the list is universal accross all phones using the list, and adapts to the phone it is connected to. Any entry for a specific phone will be omitted on that phone for example if we have three phones (Tracey, John and Jane) on our list:
There are several different functions possible. For example:
Toggle Button. A toggle or switch button can be used to log on or off of a queue, or to turn on or off a function (e.g. Follow Me) while providing a visual indication of the current settings.
Speed Dial. A speed dial button can be used to call a remote phone number NOT on the system. A phone on the system would be connected by BLF. Speed dials can be used to call or transfer to remote locations or internal queues, and ring groups (for example to "sales" instead of a specific sales person).
BLF or Busy Lamp Field. A BLF button shows the current status of the monitored extension i.e. if they are on a call, or ringing. One button can be used to view the current status of the other extension, to transfer calls to them, or to pickup a call which is ringing for them.
Cisco and Yealink phones have some significant differences in operation and capabilities.
Yealink BLF buttons must be configured as either Blind or Attended transfer targets. For details please see the related document below. With Yealink, if you have a button for a phone, you can use the same button with prefix dialing (for example, you can prefix that button with a * for a voicemail transfer.
Cisco (by virtue of having two separate transfer buttons) can always be used in either Blind or Attended mode, however, they can not be prefixed like the Yealink.
Cisco SPA500DS, Cisco SPA504, Cisco SPA514G, Cisco SPA525G2, Yealink SIP-T48G, Yealink SIP-T29G, Unlisted Phone, Fanvil X4G