This is the window that provides the controls needed to originate or answer a call and check voice mail.
The voice mail button as well as the answer button will only be available if your account on the Phone Server has a virtual voice mail box assigned to it. The answer button will only be visible if an incoming call is presenting itself.
The top sunken control is contains the phone number, the city of origin, and the time difference between you and the actual phone you are using.
The next sunken control contains control messages sent from the Phone Server and indicates various error conditions.
The blackend windows (indicated with the word suppressed) are where sound will be drawn when a call is established as well as the mixer sliders for your local sound. If you find the remote party has trouble hearing you, you may need to reduce the microphone output since the audio you send may be too loud.
The slider immediately beside your local audio control is the equivilent mixer control on the remote host (Phone Server). Once again, you can adjust the sound to improve the audio quality of the conversation.