This type of button can be used to monitor the status of another user. The button lamp indicates the status of the user.

Off = Available
Pressing the button will make a call to the user. In addition to calling the user, you can use the user button to transfer calls to the user or to start a conference with the user.
Slow Flash = Ringing
Pressing the button will display options to pickup the call.
Fast Flash = On a Call
Pressing the button will display a number of options:
Call - Call the user.
Message - Cause a single burst of ringing on the user's phone. They will also see the message "Please Call" followed by your extension number.
Voicemail - Call the user's voicemail mailbox to leave a message.
Auto Callback - Set an automatic callback on the user. The callback will occur when the user ends their current call.

The following options are only available if configured for you by your system administrator:

Drop Call - Disconnect the user's current call.
Acquire - Seize the user's current call.
Intrude - Join the user's current call, turning it into a conference call.
Listen - Start silent monitoring of the user's call.