private static extern UInt32 RasGetEntryProperties(

    Private Shared Function RasGetEntryProperties(ByVal lpszPhoneBook As String, _

Call RasGetEntryProperties beforehand, passing to it a null RASENTRY to get the correct buffer size (dwEntryInfoSize below).

    uint i = RasGetEntryProperties(null, "", IntPtr.Zero, ref dwEntryInfoSize, IntPtr.Zero, IntPtr.Zero);