Enables you to put on hold other users who are currently
    participating in a conversation with you. When you enter the
    HOLD command, everyone who is currently on the phone with you
    (including anyone who has you on hold) is placed on hold. A
    message is sent to each terminal indicating that the user has
    been placed on hold.
    You can make calls to other users while you have someone on hold.
    Format
      HOLD