Line Keys: Allow you to select a line to dial out from or to resume a call you have on hold.
Soft Keys: Stuff like History, Do Not Disturb, Directory, etc.
Volume: Adjusts the volume (ringing and while on the phone)
Loud Speaker: Places a call on loud speaker (or “speakerphone”)
Voicemail: Allows you to edit your voicemail and check messages.
Directory: Stores contacts and lists the extensions of other people.
Hold (Private): Places a call on hold. (Private hold, just for your extension)
Transfer: Allows you to transfer calls.
Conference: Initiates the conferencing function.
Headset: Turns on or off the connection to a wired or wireless headset.
Mute: Mute button while on a call, otherwise Do Not Disturb.
Extension Keys: Allows you to select an extension to dial or a call parking slot.