VMS Help PHONE, Qualifiers, /SWITCH_HOOK  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /SWITCH_HOOK="character"

    Specifies the Phone Utility switch-hook character (%).  The
    switch-hook character must be entered before each Phone utility
    command that is entered during a conversation.

    PHONE commands are terminated by pressing RETURN or by entering
    the switch-hook character. Text typed without the switch-hook
    character is considered part of the conversation. You can use
    any nonalphanumeric character as the switch-hook character.
    Enclose the character in quotation marks. The default switch-hook
    character is the percent sign (%).