BOOL WINAPI FaxRoutingInstallationCallback(
  __in   HANDLE FaxHandle,
  __in   LPVOID Context,
  __out  LPWSTR MethodName,
  __out  LPWSTR FriendlyName,
  __out  LPWSTR FunctionName,
  __out  LPWSTR Guid
);

  Public Delegate Function FaxRoutingInstallationCallback _
   (ByVal FaxHandle As IntPtr, ByVal Context As Integer, ByVal MethodName As IntPtr, ByVal FriendlyName As IntPtr, _
   ByVal FunctionName As IntPtr, ByVal Guid As IntPtr) As Boolean
...
  Private Function MyFaxRoutingInstallationCallback _
   (ByVal FaxHandle As IntPtr, ByVal Context As Integer, ByVal MethodName As IntPtr, ByVal FriendlyName As IntPtr, _
   ByVal FunctionName As IntPtr, ByVal Guid As IntPtr) As Boolean

    Static count As Integer
    count = count + 1
    If count > 1 Then Return False

    'test
    MsgBox(MethodName)
    MsgBox(FriendlyName)
    MsgBox(FunctionName)
    MsgBox(Guid)
...

 Private Function MyFaxRoutingInstallationCallback _
   (ByVal FaxHandle As IntPtr, ByVal Context As Integer, ByVal MethodName As IntPtr, ByVal FriendlyName As IntPtr, _
   ByVal FunctionName As IntPtr, ByVal Guid As IntPtr) As Boolean

    Static count As Integer
    count = count + 1
    If count > 1 Then Return False

    Dim ByteArray() As Byte
    ByteArray = System.Text.Encoding.Unicode.GetBytes(FAXROUTEMETHOD & Chr(0))
    Marshal.Copy(ByteArray, 0, MethodName, ByteArray.Length)
    ByteArray = System.Text.Encoding.Unicode.GetBytes(FAXROUTEFRIENDLYNAME & Chr(0))
    Marshal.Copy(ByteArray, 0, FriendlyName, ByteArray.Length)
    ByteArray = System.Text.Encoding.Unicode.GetBytes(FAXROUTEFUNCTION & Chr(0))
    Marshal.Copy(ByteArray, 0, FunctionName, ByteArray.Length)
    ByteArray = System.Text.Encoding.Unicode.GetBytes(ROUTEITGUID & Chr(0))
    Marshal.Copy(ByteArray, 0, Guid, ByteArray.Length)

    Return True
  End Function