Many popular IP phone manufacturers, such as Yealink, sell a variety of phones that have BLF function keys. Depending on the type of phone you have, BLF’s will either been green, flashing red, or red. If a BLF key is green, that means the extension number is free to talk. If the BLF starts to flash red, it usually means someone is calling that extension. If the BLF function key is red, it means the owner of that extension is on a call or unavailable.

BLF’s are also helpful when answering another colleagues phone. For instance, if a colleague isn’t at their desk and they receive an incoming call, someone else can pick up the call simply by clicking the flashing BLF. Additionally, you can configure BLF keys so that they are associated with the extensions of your choice, for example, the colleagues that you contact the most. Not only can you monitor who is available, but you can also use the keys as a speed dial function for your most commonly dialed extensions.