Color indication: The green light is on or off means the user is available (you can manually set the green light is on or off when you are free ), The red light flashing means there is an incoming call; The red light is always on means the user is on a call; In addition, currently only the SFB (Skype for Business) Voip Phone can indicate a yellow light, which means that the user is walkaway ^^ Red Light flashing means there is an incoming call, and the red light is always on means the user is on a call, then people would not interrupt you ^^ Yellow light, In addition, currently only the SFB (Skype for Business) VoIP Phone supports a yellow light, which means the user is walkaway ^^ Green Light is on/off means the user is available (Supports manually setting the green light is on/off to indicate you are idle) ^^ The busy light connects via a 2.5 mm jack and is fully compatible with the following devices (this is the complete list of supported models): MP50, MP54 USB Phone, WH62, WH64, WH68, WH63, WH63 E2, WH66, WH67, WH64 WS, WH68 WS DECT Wireless Headset, and BH71 Workstation Bluetooth Headset