Library /sys$common/syshlp/phonehelp.hlb DIAL, Parameter  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 [node::]username

    Specifies the name of the user to be phoned and their node (if
    their node is not the same as your current node). Node numbers
    cannot be entered when you are calling someone on another node.
    DECnet access strings are allowed.